Phase equilibria in the Co-Cr-W system with special emphasis on the R-phase

M E T A L L O G R A P H Y S , 515-541 (1972)

515

Phase Equilibria in the Co-Cr-W System with Special Emphasis on the R-Phase R. G. BARROWS U.S. Army Air Mobility R & D Laboratory, NASA-Lewis Research Center, 21000 Brookpark Road, Cleveland, Ohio 44135 AND

J. B. NEWKIRK* Department of Chemical Engineering and Metallurgy, University of Denver, Denver, Colorado 80210

The equilibrium phases at 1350~C were studied in twenty-one ternary or binary alloys in the Co-Cr-W system. Three topologically close-packed phases were found, one of which is a new phase which is isomorphous with the prototype R-phase in the Co-Cr-Mo system. The crystallographic verification of the Co--Cr-W R-phase is given, including comparisons of observed and calculated d-spacings and line intensities. Also, certain metallographic characteristics of the R, tz, a, and 0t-Co phases are described, with special emphasis on the response of these phases to potentiostatic electrolytic etching. A ternary phase diagram for the Co-rich region at 1350°C is proposed which is consistent with the data obtained in this study and with most other published work relating to this system.

Introduction I n 1970 at the Second International Conference on the Strength of Metals and Alloys [1] we presented a brief and preliminary description of a new intermetallic phase which we found in the C o - C r - W system. T h e present paper is intended to provide further evidence for the existence of this phase (called Rphase), to document its crystallographic and metallographic properties when it occurs in a matrix of face-centered cubic (FCC) alpha-cobalt, and to show its metallographic relation to other phases that are known to occur in this important ternary system. We have reported that the R-phase in the C o - C r - W system is isomorphous with a phase of the same designation in the C o - C r - M o system [2]. At 1350°C it is stable over a narrow composition range approximating Co~zCrzsW15, and has a complex hexagonal unit cell with a o ~ 10.882A and co __ 19.254 A * Brainerd F. Phillipson Professor. Copyright © 1972 by American Elsevier Publishing Company, Inc.

516

R. G. Barrows and J. B. Newkirk

depending on the exact composition. Referred to a rhombohedral lattice, the parameters are approximately a 0 = 8.981 A and ~t = 74° 34.5' (space group C2i--R3). The approximate composition ranges of stability of the new phase with respect to other known phases in this ternary system at 1350°C are given in Figs. 1 and 9. In the paragraphs which follow, details are given which supplement and support these essential facts. Microstructural characteristics of the R-phase, in conjunction with other phases found in this system, are also given. Examination of the Co-W system reveals that face-centered cubic (FCC) ~-Co,/~-phase and body-centered cubic (BCC) tungsten can exist at 1350°C [3]. The Co-Cr binary diagram shows that FCC ~-Co, 8-phase and BCC-Cr are possible [3]. At temperatures below 1310°C a ~-phase also exists in the Co-Cr system. The W-Cr system has a miscibility gap and at 1350°C where BCC-W and BCC-Cr can coexist [3]. The /~ and ~ phases belong to a group of transition metal intermetallic compounds that have been characterized [4] as topologically close-packed (TCP). They are hard, brittle and crystallographically complex. The R-phase is also a member of the TCP-type family of phases. Information regarding the Co-Cr 8-phase is not extensive. Previous work on the Co-Cr-W system includes that by K6ster who proposed a room temperature diagram following slow cooling of the alloys [5]. Goldschmidt proposed a 600°C diagram which showed the TCP/~ and ~ phases to project into ternary space [6]. Lobl, et al., postulated a ternary Co-Cr-W diagram at 700°C and found a ternary BCC phase which they designated as the N-phase [7]. Drapier, et al., [8], established a portion of the FCC ~-Co boundary at 1200°C in studies of the nature and morphology of intermetallic compounds formed when the refractory metals W, Mo, Ta, and Cb were individually added to Co-Cr alloys. After aging high C r + W content alloys at temperatures ranging from 600°C to 1000°C, a tetragonal phase was discovered with the approximate composition Co4Cr3W and with lattice parameters: a 0 = 6.55 ~ and co - 4.71 ~t. It was pointed out by the authors that this phase might be the N-phase that had been reported by Lobl, et al.

Experimental Button size melts (from 15 to 30 g, depending primarily on tungsten content) were made by arc-melting high purity elements t on a copper hearth under zirconium-gettered argon at one atmosphere pressure. Tungsten powder, consisting of particles 10-20/~ in diameter, was placed at the bottom of the melting cavity and lumps of cobalt and chromium were carefully placed on top. Loss of tungsten by arc blowing was thereby minimized. The arc was operated 1 Purchased from the United Mineral and Chemical Corporation and reported to contain less than 0.001% impurities each.

The Co-Cr-W System

517

approximately 5 sec for each melt. Each button was turned over and remelted five times to achieve homogeneity. Final weight losses were always less than 1 °/o. Chemical analysis of the melted buttons, made by a method described below, showed that almost all the loss consisted of chromium, undoubtedly due to its high vapor pressure. As melting experience was gained it was possible to compensate for chromium losses by altering the charge composition slightly. Table 1 lists the charge compositions of the alloys investigated. TABLE 1 Experimental Co-Cr-W Alloy Compositions

Alloy A B C D

E F G H I J K

Charge Composition: w/o, (a/o) Co Cr W 37.42 (48.01) 42.68 (58.69) 30.43 (46.99) 35.06

(62.75) 50.24 (47.11) 48.15 (52.11) 41.51 (53.38) 36.20 (51.29) 33.05 (49.58) 27.52 (45.17) 21.88 (37.96)

25.17 (36.61) 14.36 (22.38) 11.44 (24.87) --

-49.76 (52.89) 33.98 (41.68) 21.54 (31.39) 17.13 (27.51) 14.94 (25.41) 12.51 (23.27) 13.19 (25.94)

37.41 (15.39) 42.96 (18.93) 58.13 (28.14) 64.94 (37.25) --17.87 (6.20) 36.95 (15.23) 46.67 (21.20) 52.01 (25.01) 59.97 (31.55) 64.93 (36.10)

Alloy L M N P Q R S T U V

Charge Composition: w/o, (a/o) Co Cr W 29.87 (43,61) 26.43 (37.74) 58.24 (74.89) 53.22 (61.13) 52.24 (64.15) 55.77 (62.61) 56.39 (63.91) 55.41 (61.60) 27.70 (43.15) 65.43 (75.70)

19.85 (32.86) 24.63 (39.87) 7.55 (11.01) 23.18 (30.18) 17.08 (23.78) 23.53 (29.94) 21.98 (28.23) 24.91 (31.38) 16.39 (28.94) 12.20 (16.00)

50.27 (23.53) 48.94 (22.40) 34.21 (14.10) 23.60 (8.69) 30.68 (12.08) 20.70 (7.45) 21.64 (7.87) 19.69 (7.02) 55.90 (27.91) 22.37 (8.30)

Heat treating was done in a horizontal globar tube furnace with longtime temperature control to about + 10°C at 1350°C. Zirconium-gettered argon gas was passed slowly through the tube and maintained at a slight positive pressure. Specimens were held in alumina boats and were quenched by dropping them into cold water. Elapsed time between removal of the specimen from the furnace hot zone until it entered the water bath was less than 2 see. Some evidence of surface loss of chromium was seen. No evidence was found of any reaction between the alumina boat and the specimen. Metallographic specimens were sectioned at least 2 m m from any surface

518

R. G. Barrows and J. B. Newkirk

that was exposed during heat treatment. The #, o, and R phases were very resistant to immersion etchants such as 5% bromine-methanol and 92HCI-5HzSO4--3HNO a. Galvanically controlled electrolytic etching (10% oxalic acid in water) was also ineffective in distinguishing the various phases. More satisfactory results were obtained by potentiostatic methods [9] using aqueous solutions of either 5% H2SO 4 or 10~/o NaOH, the latter being preferred. Details relating to optimum applied potentials are given in a later section. Here it is enough to say that for a given temperature and electrolyte the dissolution of a specific phase (i.e. its etching tendency) in a multiphase alloy is dependent upon the applied potential between the specimen electrode and the solution. The 0~ and o phases behaved alike with respect to their dissolution in both the sulphuric acid and the hydroxide electrolytes. However, enough difference existed to enable them to be clearly distinguished metallographically. The same was found to be true for the/~ and R phases. All micrographs were made with bright-field Kohler illumination unless otherwise noted. A nine-point grid was used to determine volume fractions of the various phases, using the point-counting method outlined by Hilliard [10]. Microhardness measurements were made utilizing a Vickers-type diamond indenter and a 50 g load. Each hardness reported represents the average of at least twenty indentations. X-ray powder samples for Debye-Scherrer patterns were obtained by one of two methods: (1) crushing the entire alloy and screening it through a 200 mesh screen, or (2) collecting residues from electrolyte dissolution of an alloy by potentiostatic techniques. For those alloys whose compositions were well within the field of stability of the topologically close-packed phases, simple crushing provided a suitable powder sample. It was possible to crush alloys containing up to about 50 volvo of the more ductile FCC ~-Co and to obtain satisfactory powder samples of the TCP phases. However a clear pattern for the ductile FCC ~-Co phase was not obtained, probably because it was removed from the samples during screening or because ~-Co diffraction lines were unobservable, having been broadened by elastic strains introduced during crushing. For alloys containing large amounts of ~t-Co as the continuous phase, electrolytic dissolution was used to extract powder samples consisting of practically 100% of the minor (/~ or R) phases. The unattacked phase was collected in the electrolytic cell and separated by centrifuging and decanting four times with distilled water. The residue was then washed in methanol and dried. An evacuated 2-radian DebyeScherrer film camera was used for making the powder diffraction patterns. Most were made using filtered CrK~ radiation. Relative line intensities were visually estimated and rated on a 0-100 scale. Very weak lines, whose existence on the film was questionable, were given an intensity value of 1. ASTM crystallographic data cards 9-52 (Co-Cr sigma-phase), 2-1091 (CoTW6 /~-phase), and 7-49 (Co-Cr-Mo R-phase) were helpful in indexing the

The Co-Cr-W System

519

TCP phase patterns found in this study. However, many more lines were observed than were included in the cards, and the card information was largely based on unit cell dimensions different from those encountered in this investigation. Therefore, to supplement the cards, a computer program [11] was utilized to calculate the complex powder patterns of the cr,/x, and R phases. Input to the program included space group, lattice constants, radiation wavelength, lattice site positions, kinds of atoms occupying the sites, and atomic scattering factors. Crystallographic data for the/x and cr structures were taken from Pearson [12], and for the R-phase from Komura, et al. [13]. The program output included Miller indices, d-spacings, intensities normalized to 100, and structure factors. Lattice constants were calculated using a Nelson-Riley function in a Cohen's least squares analysis. The difference between measured and calculated (best-fit regression lines) sin 2 0 values for each d-spacing provided a measure for the correctness of indexing. A sin s 0 difference of 10 .6 was considered marginally acceptable. A Phillips AMR/3 electron probe microanalyzer was used for quantitative analysis of the alloy phases. A computer program formulated by Colby [14] was used to convert raw X-ray intensity data to quantitative results, with an accuracy estimated at 2 4 % of the amount present.

Results and Discussion Portions of the Co-Cr-W phase diagram at 1350°C were established by examination of the alloys listed in Table 1. Figure 1 shows the phase field configurations established in this investigation together with experimental alloy compositions. Compositions within the dashed-line regions were not examined. The diagram has been completed only to show that the findings of this study, together with the known binary phase diagrams, are consistent with the requirements of the phase rule in ternary phase diagram construction [15]. As-ca~t alloys were heat treated at 1350°C for 44 h and water quenched. This treatment was found to be satisfactory in bringing as-cast alloys to a condition nearing equilibrium since no significant microstructural differences were noted in like specimens that had been held at 1350°C for 24 and 210 h, respectively. Electron microprobe scans across various phases showed no detectable concentration gradients for cobalt, chromium or tungsten after homogenization. Although the evidence indicated that practical equilibrium was reached for each alloy, it is suspected that equilibrium was only approached for compositions high in TCP phase content such as in alloy A and H. Since the TCP phases contain greater amounts of tungsten than FCC co-Co, and since these structures are very closely and efficiently packed, it is reasonable to suspect that diffusion would be slower than in alloys consisting mostly of ~c-Co.

R. G. Barrows and aT. B. Newkirk

520

Potentiostatic polarization curves for the /z, (r, R, and or-Co phases were established, using single phase or nearly single phase specimens of/~, o, R, and ~t-Co. The curves obtained in two different electrolytes are shown in Figs. 2(a) and 2(b). Note that o or ~t-Co phases could be preferentially dissolved from alloys containing the # or R phases. No electrolyte or potential range was found which could preferentially dissolve # from R or vice versa. However, X-ray powder samples of the/~ or R phases could readily be obtained from two-phase specimens whose major constituent was ~-Co or ~-phase. W

1350°C

F :

e=

,,

:/

\

Co

/

X .cc-c.

CR WEIGHT %

Fro. 1. Isothermal section of the Co-Cr-W phase diagram at 1350°C in wt o/Jo, showing experimental alloy compositions. Potentiostatic dissolution was especially useful in metallographic etching. Using an electrolyte of 10% NaOH in water and potential of about 200 mV (S.C.E.)I--a color difference between the/z and R phases in the same specimen was always produced. The color of a given phase appears to be due to light interference rather than to the intrinsic color of the reaction product. Figure 3 shows an example of a microstructure consisting of ( ~ + / ~ + R ) phases in an alloy that was quenched from 1350°C. Remnants of the cast structure are still apparent, although longer heat treatments produced no changes of phase ] Saturated calomel electrode.

The Co-Cr-W System

52t

T

60

5"&

HtSO4

ELECTROLYTE

50 o w o.

40

~ ~o

,L.A /

.J

~ 20 ,4

d

tO

• 1000

,1250

*1500

,1750

POTENTIAL VS. S.G.E. (MILLIVOLTS)

(a)

10%

ELECTROLYTE

40

/

m 3O .4 .J

i

/

5O

N n: w

NAOH

20

,4

O

10

a

-250

MU& R ~ PHASES

':!:?

L

I

~

0

250

500

POTENTIAL VS. S C . E

.,,

(MILLIVOLTS)

(b) FIG. 2.

Potentiostatic dissolution behavior o f the c(, o,/L and R phases o f the C o - C r - W

system in (a) 5% H2SO4 and (b) 10% N a O H aqueous electrolytes. 37

522

R. G. Barrows and J. B. Newkirk

compositions and amounts. This etching method permitted the unambiguous indentification of phases in all of the alloys because, once an optimum potential had been determined, identical etching behavior of a given phase could be achieved from specimen to specimen. A persistent gray phase (about 0.3 vol °/o) in all the alloys was identified as Cr203 by X-ray diffraction of extraction residues and by electron probe microanalysis in situ. Shrinkage porosity, visible as black voids, varied with TCP-phase content; from about 15% by volume for alloys consisting mainly of TCP phases to zero ~o for alloys containing less than 50 volc}/o T C P phases.

FIG. 3. Alloy J potentiostatically etched at 200 mV (S.C.E.) with 10% NaOH electrolyte. Dark areas are tz-phase, gray is R and white ~-Co, black areas are voids. Mag. 1 80 ×. Three initial exploratory alloys, designated A, B, and C, were made at compositions anticipated to be well within T C P phase regions of the ternary phase diagram. Photomicrographs in Fig. 4 show that each alloy contained two phases. There was about 15 vol °/o porosity in alloys A and C due to shrinkage upon solidification. The gray constituent of alloy B and the major phase of alloy C had microhardnesses of about 1200 kg/mm 2 for a 50 g load. The overall alloy A also had microhardnesses of about 1200 kg/mm 2. The light etching phase in alloy B and the minor phase in alloy C had microhardness of about 350 kg/mm ~. The Debye-Scherrer pattern of the/x-phase was readily identified in powder patterns made from alloys B and C, with a o ~ 4.743 • and co = 25.54/~. Most of the pattern made with the alloy A powder indexed to a ~ structure with unit cell parameters a o = 8.858 A and co ~ 4.577A. However, several prominent lines were present which fit neither the ~ nor the /z structures. Three of the unknown lines resembled a similar sequence of strong lines in the Co-Cr-Mo

The Co-Cr-W System

523

(a)

(b) ~ ,

~

.

~

.

.

.

.

.

.

~

.

.

.

.

.

.

:.

.

.

.

.

(c) FIo. 4. Alloys A, B and C, after 44 h at 1350°C, (A) R-phase (minor constituent) in o-phase, 92% HCI, 5% H2SO4, 3% HNO3; (B) /~-phase (gray) in a continuous g-Co matrix, 92% HCI, 5% H~SO4, 3°/0 HNO3; (C) g-Co (minor constituent) in /~-phase; dark areas are voids. Mag. 600 × ; 10% NaOH (aq.), 200 inV.

R. G. Barrows and J. B. Newkirk

524

R - p h a s e pattern [16]. U s i n g hexagonal lattice parameters based on these three lines, all the previously unidentified lines could then be indexed to the R structure. Potentiostatically controlled digestion of alloy A in a sulphuric acid electrolyte at a potential of 1200 m V (S.C.E.), see Fig. 4a, resulted in the extraction of the m i n o r R-phase. A p p r o x i m a t e l y 55 X - r a y reflections assignable to the R - s t r u c t u r e were obtained (see T a b l e 2). TABLE 2 Comparison of Calculated X-Ray Powder Diffraction Pattern for a C o - C r - W R-Phase ~ Using Chromium K~ Radiation and Observed Powder Patterns for Electrolytic Extracts from Alloys A and P

Calculated X-Ray Pattern ~ Line d-Space Hexagonal No. Angstroms I hkl

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

8.4644 6.7343 6.4179 5.4409 4.5769 4.2866 4.2322 4.1502 3.5646 3.5025 3.3672 3.3406 3.2089 3.1413 2.9817 2.8632 2.8215 2.7640 2.7205 2.6404 2.6148 2.5900 2.5224 2.5047 2.3754 2.3386 2.3319 2.2969

7.4 1.2 0.9 0.4 0.0 9.0 9.7 15.2 2.6 7.4 0.4 19.0 0.2 1.3 0.3 3.6 2.6 9.6 0.4 0.6 9.1 9.0 2.1 5.1 0.8 18.3 0.5 13.3

101 012 003 110 021 104 202 113 015 211 024 122 006 030 205 214 033 116 220 107 125 131 312 223 027 401 018 134

Observed X-Ray Patterns CrK~ = 2.29092 A Alloy A Alloy P d-Space d-Space Angstroms I Angstroms

8.3664

10

4.2586 4.2029 4.1293 3.5506 3.4891

2 3 7 3 3

4.2612 4.2092 4.1290 3.5499 3.4875

10 12 15 9 10

3.3281

15

3.3261

30

3.1304

2

2.8551 2.8104 2.7550

7 5 20

18 20 2 10 10 30 30

2.7546

7

2.6067 2.5821

7 10

2.3318

7

2.6079 2.5819 2.5178 2.4988 2.3665 2.3331

2.2917

7

2.2923

525

The Co-Cr-W System TABLE 2 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77

2.2885 2.2448 2.1770 2.1626 2.1485 2.1433 2.1393 2.1161 2.1095 2.0751 2.0565 2.0097 1.9942 1.9909 1.9722 1.9584 1.8947 1.8864 1.8852 1.8578 1.8497 1.8136 1.7893 1.7823 1.7734 1.7705 1.7682 1.7550 1.7513 1.7453 1.7314 1.7209 1.6998 1.6938 1.6929 1.6861 1.6836 1.6816 1.6703 1.6670 1.6408 1.6165 1.6083 1.6045 1.5968 1.5789 1.5709 1.5707 1.5548

0.3 3.3 100.0 70.8 0.0 0.0 4.6 11.2 76.9 0.1 61.9 47.1 40.8 27.8 28.0 12.9 2.4 10.3 9.4 0.5 2.9 0.0 0.0 1.1 7.8 0.5 0.1 0.6 0.8 0.8 3.1 0.0 0.1 0.0 1.7 0.2 0.2 0.5 0.6 0.2 0.0 0.3 1.0 0.8 0.0 0.7 0.9 0.5 0.0

042 036 217 315 321 208 009 404 232 226 140 045 128 119 324 143 137 1.0.10 235 051 502 330 407 0.2.10 241 318 039 054 422 333 146 0.1.11 327 2.1.10 505 511 048 229 244 152 2.0.11 425 238 0.0.12 514 336 1.2.11 060 057

(Continued) 2.2382 2.1722 2.1576

5 70 50

2.2410 2.1731 2.1587

10 100 95

2.1049

60

2.1364 2.1124 2.1059

15 15 95

2.0519 2.0055

50 50

2.0529 2.0061

90 85

1.9897

60

1.9899

90

1.9680 1.9547

30 15

1.9691 1.9553 1.8928

50 25 2

1.8831

30

1.8835

45

1.8464

7

1.8477

15

15

1.7714

30

1

1.7300

10

1.6917

5

1.7710 '

1.7287

R. G. Barrows and J. B. Newkirk

526 TABLE 2

Calculated X-Ray Pattern" Line d-Space Hexagonal No. Angstroms I hkl 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118

1.5502 1.5502 1.5443 1.5389 1.5296 1.5256 1.5090 1.4949 1.4909 1.4839 1.4826 1.4748 1.4690 1.4631 1.4543 1.4415 1.4379 1.4373 1.4332 1.4316 1.4289 1.4214 1.4129 1.4107 1.4050 1.3845 1.3834 1.3820 1.3771 1.3675 1.3656 1.3608 1.3604 1.3602 1.3499 1.3469 1.3464 1.3430 1.3333 1.3307 1.3202

0.1 0.6 0.8 3.5 4.5 2.4 2.4 8.6 0.1 0.4 3.4 0.4 6.7 0.4 1.5 2.6 3.0 0.9 0.0 1.8 0.6 13.2 3.1 8.3 4.3 1.8 5.5 0.6 4.0 3.0 17.3 0.5 9.2 4.6 0.2 0.6 0.2 12.0 0.6 1.5 0.4

1.3.10 155 431 1.1.12 342 063 250 247 4.0.10 508 149 434 253 1.0.13 3.1.11 517 3.2.10 345 161 428 0.3.12 612 0.2.13 066 0.4.11 158 339 2.2.12 164 2.1.13 256 0.1.14 2.3.11 440 437 0.5.10 615 701 072/532 443 2.0.14

(Continued) Observed X-Ray Patterns CrKa = 2.29092/~ Alloy A Alloy P d-Space d-Space Angstroms I Angstroms

1.5385 1.5272

10 10

1.5375 1.5283

20 20

1.5073 1.4944

2 15

1.5083 1.4940

10 35

1.4823

7

1.4818

15

1.4679

10

1.4682

20

1.4540 1.4408

5 10

1.4208 1.4126 1.4101 1.4047

45 5 20 15

1.4203

215

1.4095

10

1.3829

10

1.3833

20

1.3761:

2

1.3647

20

1.3767 1.3674 1.3652

15 3 45

1.3597

20

1.3600

40

1.3423

15

1.3426

40

527

The Co-Cr-W System TABLE 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167

1.3074 1.3039 1.3027 1.2965 1.2950 1.2886 1.2836 1.2830 1.2826 1.2738 1.2712 1.2709 1.2661 1.2650 1.2612 1.2539 1.2524 1.2493 1.2484 1.2482 1.2375 1.2339 1.2331 1.2253 1.2219 1.2171 1.2167 1.2092 1.2070 1.2043 1.2017 1.1973 1.1937 1.1882 1.1877 1.1873 1.1804 1.1758 1.1749 1.1704 1.1693 1.1675 1.1659 1.1645 1.1633 1.1608 1.1604 1.1601 1.1517

0.6 2.1 0.9 21.3 2.5 0.1 12.6 38.8 0.2 0.7 2.5 48.6 41.0 25.4 1.7 0.2 1.8 0.4 0.6 46.9

23.3 4.8 75.4 13.1 65.5 12.0 0.5 32.4 12.0 7.4 16.5 3.0 2.8 5.2 0.3 15.9 0.4 0.0 18.5 1.0 0.6 13.4 0.2 0.0 1.2 0.1 1.6 0.6 7.0

2.4.10 621 348 354/704 262 1.3.13 0.0.15 1.2.14 5.0.11 167 5.1.10 075/535 069 1.4.12 624 4.0.13 446 1.1.15 4,2.11 170 265 618 259 173 3.2.13 3.1.14 1.5.11 357/707 4.3.10 541 3.3.12 452 1.0.16 0.3.15 0.4.15 360 627 081 078/538 544 802 363 0.2.16 0.5.13 176 2.2.15 2.3.14 3.4.11 1.6.10

2

(Continued) 1.3029

4

1.3033

2

1.2960

40

1.2963

55

1.2830

90

1.2830

60

1.2705

70

1.2707

60

1.2654

100

1.2659 1.2649

50 40

1.2521

5

1.2478 1.2373

50 20

1.2481 1.2373

60 45

1.2328

90

1.2330

80

1.2248 1.2217 1.2169

15 90 25

1.2250 1.2218 1.2170

20 75 30

1.2088

40

1.2041 1.2017

2 25

1.2091 1.2070 1.2043 1.2017 1.1970 1.1937 1.1880

55 50 15 40 10 5 4

1.1869

20

1.1871

45

1.1747

25

1.1749

50

1.1673

20

1.1674

45

528

R. G. Barrows and J. B. NewMrk TABLE 2 (Continued)

Calculated X-Ray Pattern a d-Space Hexagonal No. Angstroms I hkl

Line

168 169 170 171

1.1514 1.1493 1.1485 1.1479

55.3 70.1 1.4 3.3

455 271 268 449

Observed X-Ray Patterns CrK~ = 2.29092 A Alloy A Alloy P d-Space d-Space Angstroms I Angstroms I 1.1513 1.1492

50 60

1.1513 1.1492

70 75

* Hexagonal unit cell with lattice constants ao = 10.8819 A and Co = 19.2356 A. An electrolytic residue of alloy P provided the best diffraction pattern for the R-phase in this investigation. The annealed alloy consisted of approximately 5 vol °/o R-phase and about 1 vol ~o sigma-phase in a matrix of FCC ~-Co. Potentiostatic dissolution of the ~-Co and a phases in the sulphuric acid electrolyte at 1200 mV (S.C.E.) provided a residue entirely of R-phase. The observed diffraction patterns for the R-phase in Alloys A and P together with a calculated R-phase powder pattern are given in Table 2. The assumptions entailed in calculating the powder pattern are given below. In calculating d-spacing, intensities and Miller indices for the proposed R-phase, the crystallographic parameters determined by Komura et al. [13] for the Co-Cr-Mo R-phase were used. (See Table 3). The composition C%aCrlsW15 was assumed for the R-phase, on the basis of electron probe microanalysis. The larger coordination sites CN-16 were considered to be occupied only by tungsten atoms, as they are by molybdenum in the Co-Cr-Mo R-phase. The smaller CN-12 sites were assumed to be occupied by Co-Cr in a 23:15 ratio. Retaining the composition Co~sCrlsW15, the remaining tungsten atoms were distributed among the CN-14 and -15 sites in amounts consistent with those found for molybdenum by Komura, et al. For the CN-14 and -15 sites, it was assumed that after tungsten was accounted for, the remaining atoms again were cobalt and chromium in the ratio 23:15. Table 3 shows the assumed atom distribution in terms of atomic % tungsten. The average atomic number (Z) of each site is also tabulated and is based on the atomic composition of each respective site. The atomic scattering factor of the hypothetical atoms occupying each kind of site was considered to correspond to the average atomic number of each site. Thus, for atom kind B1, in Table 3, the average Z is 44.1 and the approximate atomic scattering factor for the element ruthenium was used. R-phase lattice parameters from alloy P are: a0 ~ 10.8819~0.0004A and co = 19.2536±0.0012 A. The difference between calculated (best-fit regression line) and observed sin ~ 0

The Cr-Co-W System

529

values was calculated for each line having 20 greater than 100 °. I n all cases that difference was well below the marginally acceptable value of 10 -6. A plot of observed (alloy P) and calculated line intensities vs d-spacings, given in Fig. 5, shows that no intensity inversions occur over the entire diffraction pattern. TABLE 3 Crystallographic Parameters (Hexagonal) for the Co-Cr-Mo R-Phase a (Komura et al. [13]) and the Assumed Configuration for the Newly Found Co-Cr-W R-Phase

Hex. Atom Position A1 A2 A3 A4 A5 A6 B1 B2 C1 D1 D2

3(b) 6(c) 18(f) 18(f) 18(f) 18(f) 18(f) 18(f) 18(f) 6(c) 18(f)

CN 12 12 12 12 12 12 14 14 15 16 16

x 0 0 0.1596 0.0509 0.9212 0.2250 0.1759 0.1132 0.0330 0 0.2671

y 0 0 0.2470 0.2790 0.1393 0.1969 0.1265 0.2687 0.2579 0 0.2218

z 1 0.3044 0.0020 0.1000 0.1962 0.2685 0.3969 0.4652 0.3183 0.0735 0.1222

Co-Cr-W R-Phaseb a/o Mo Zlssura. a/o W Zas.um. 11 0 0 0 11 0 62 53 76 100 100

26.8 25.0 25.0 25.0 26.8 25.0 35.2 33.8 37.5 41.5 41.5

0 0 0 0 0 0 37.9 32.4 46.4 100 100

25.8 25.8 25.8 25.8 25.8 25.8 44.1 41.4 48.2 74.0 74.0

Space Group C2i-R3. Assumed occupancy and atomic number for sites in the CoiaCrlsWls R-phase. At sites with no tungsten, it was assumed that cobalt and chromium atoms occupied these sites in the ratio of 23 to 15. For sites partially occupied by tungsten, it was assumed that the remaining atoms, after tungsten was accounted for, were cobalt and chromium also in the ratio 23 to 15. For atom kind B 1, the effective atomic number would be: Effective At. No. (B 1) : (0.379)(74)+(15/38)(1--0.379)(24)+(23/38)(1--0.379)(27) = 44.1. T h e compositions of conjugate phases given in Table 4 are estimated to be accurate to 2 ~ w/o of the amount present [14]. Estimations were made of the total alloy compositions of several alloys by adding the amounts of each element contributed by each phase present. First the vol ~o of phases present in selected alloys were determined by quantitative metallography. Table 5 gives the results for alloy A as an example (see Fig. 23) where the vol ~o of the R, (7, and pores are given. Knowing the chemical compositions (Table 4) and lattice parameters (Table 7) of the cr and R phases, an idealized density (no lattice vacancies) was calculated. Reasonable values of the relative amounts of the phases present in wt °/o were then computed and are given in Table 5. From the weight percentages of the phases present and the chemical compositions of the phases, the total

530

R. G. Barrows and J. B. Newkirk

alloy composition was calculated. Table 6 shows excellent agreement between the composition of alloy A, determined in the above manner, and the actual charge composition. This procedure gave equal consistency between measured and charge compositions for all the other alloys. Lattice parameters of the R-phase and of other phases found in selected alloys are shown in Table 7. They are based on Cohen's least squares analysis and are i00 OBSERVED

>-

--

-

CALCULATED

-

75

u3 Z LIJ F-Z

50 N

/

/

I

fL

__

!

zo 25

./

/

/'

,",i ¸

,,L • ,

~

L I~

~

.

,[

I I 45

i40

I 35

I 30

OBSERVED

I 25

I

I

120

I.~

,

D- S P A C I N G S

(~) IOO ----,-h

.

.

.

.

.

~s

/"!I b\ OBSERVED

75

,'

[I

CALCULATED . . . . .

z z a

5o

J ,,(

j'i

jl

,,

i ¸ "I

~,

, I'

~,]'

z~ OBSERVED

,~

JJ

i~

,l.a

D-SPACINGS

(b) FIO. 5. No intensity inversions occur over the entire Debye-Scherrer spectrum for the proposed R-phase extracted from alloy P.

The Co-Cr-W System

531 TABLE 4

Chemical Compositions of Conjugate Phases in C o - C r - W Alloys Equilibrated at 1350°C.

Alloy A

B

C

D E F

G

H

I

J

K

L

M

N

P

Element Co Cr W Co Cr W Co Cr W Co W Co Cr Co Cr W Co Cr W Co Cr W Co Cr W Co Cr W Co Cr W Co Cr W Co Cr W Co Cr W Co Cr W

~

Composition (w/o) /z cr 39.9 26.6 33.5

59.2 18.0 22.8 59.5 18.0 22.5 62.7 37.3

56.8 31.7 11.5 56.8 23.4 19.8 56.9 22.9 20.2 56.6 22.8 20.5 57.2 22.0 20.8

19.6 61.0 62.4 7.8 29.8 56.5 24.1 19.4

R 29.6 16.3 54.1

23.3 7.8 68.9 23.8 8.4 67.8 29.1 70.9 50.7 49.3 42.7 36.0 21.3 40.2 24.9 35.0 23.5 10.2 66.3 23.5 10.2 66.3 24.2 10.0 65.8 21.2 11.9 66.9

19.4 31.5 38.1 28.0 3.5 58.5

33.2

29.3 15.0 55.8 28.6 14.6 56.8 28.5 14.5 57.0 28.7 14.1 57.2

35.4 28.6 35.9 30.4 18.5 58.5

25.8 17.2 57.0 23.0

40.4 26.4 53.8

29.9 16.3

R. G. Barrows and J. B. Newkirk

532 TABLE 4

Alloy

Element

g

Q

Co Cr W Co Cr W Co Cr W Co Cr W Co Cr W Co Cr W

59.9 18.7 21.4 56.4 23.6 20.0 57.1 22.0 20.9 56.2 25.0 18.8

R

S

T

U

V

(Continued) Composition (w/o) ~ o

R

25.6 9.2 65.2 40.7 a 26.5 ~ 32.8 ~

29.5 ~ 16.1 ~ 54.4 ~

24.8 ~ 9.8 ~ 65.4 ~

28.6 15.3 56.1 65.9 12.1 22.0

a No difference in compositions for 1350°C and 1380°C equilibration temperature. TABLE 5 A m o u n t s of Phases Present in Alloy A Vol % Disregarding Porosity

Constituent

Vol %

Pores R-Phase o-Phase

18.25 + 1.38 15.95 + 1.16 65.80+ 1.28

. . . 19.51 _ 1.48 80.49 + 1.89

X-Ray Density (gm/cm3) .

. . . 12.0408 10.1313

Phase Wt % .

. 22.36 + 1.69 77.64 + 1.82

TABLE 6 Comparison of Calculated and Charge Compositions of Alloy A

Element

Charge Composition (w/o)

Calculated Alloy Composition (w/o)

Difference (w/o)

Co Cr W

37.42 25.17 37.41

37.95 24.59 37.45

-0.53 +0.58 - 0.04

The Co-Cr-W System

533

reported for a 95% confidence level. T h e phases identified in the alloys are consistent with the phase diagram shown in Fig. 1. Neither the low-temperature H C P E-Co nor the hexagonal y-CoaW phase was found in any of the alloys [3]. No evidence of a Co-Cr 8-phase was detected. T h u s there were no lines in the patterns that could not be indexed to one of the C o - C r - W phases listed or to the presence of Cr20 a. TABLE 7 Lattice Parameters of Phases from Selected Alloys

Alloy

Phase

Crystal System

A

R o tt /t o R o R tt R o R p. o # R

Hex. Tet. Hex. Hex. Tet. Hex. Tet. Hex. Hex. Hex. Tet. Hex. Hex. Tet. Hex. Hex.

B D E G J L M

N P

Lattice Parameters ao 10.8819+0.0007 8.8579 + 0.0058 4.7428 -+0.0040 4.7398_+0.0017 8.7482 + 0.0033 10.8827 + 0 . 0 0 4 8 8.8610 _+0.0056 10.8902+0.0020 4.7337_+0.0014 10.8971 _+0.0017 8.8593 + 0.0090 10.9346 _+0 . 0 0 1 6 4.7466 + 0 . 0 0 0 7 8.8996 _+0.0024 4.7362 _+0 . 0 0 0 7 10.8819_+0.0004

(A) Co

19.2593+0.0022 4.5772 + 0.0035 25.5421+ 0.0108 25.5421+_0.0107 4.5352 +-0.0018 19.2586+ 0.0076 4.5781 + 0.0021 19.2613+-0.0050 25.5347+-0.0132 19.2812+-0.0053 4.5806 +-0.0095 19.3530+ 0.0044 25.6599+ 0.0049 4.6000 +-0.0012 25.5465+ 0.0047 19.2536+-0.0012

T o establish whether the C o - C r - W R-phase is stable above and below 1350°C, alloys R, S, and T , consisting of a F C C s-Co matrix with the R, /x, or o phase respectively as a second phase, were examined after annealing at temperatures other than 1350°C. T h e alloys were given an initial heat treatment at 1350°C for 210 h. Table 8 shows that after heat treating these alloys at 1380°C for 150 h, the vol °/o of the minor phases was significantly lower. Thus, the ~t-Co TABLE 8 Vol % of Minor Phases After Heat Treatment at 1350°C and 1380°C, Respectively

Alloy

Minor Phase(s)

R

R o # a

S T

Vol % of Minor Phase 1350°C (210 h) 1380°C(150 h) 8.0 1.7 2.9 2.7

3.8 1.4 2.2 0.0

R. G. Barrows and J. B. Newkirk

534

solvus boundary must slope toward decreasing solubility with lowering temperature for each of the three phases. After the 1380°C heat treatment, the alloys were aged at 1200°C for times of 1, 10, 100, and 1000 min. Alloy R, which at 1380°C, was very near the 0 ~ + R + a field, showed signs of sigma-phase decomposition after 1000 min. [See Fig. 6(a).]

(,0

(b)

(c) Fro. 6. (a) Alloy R: ~-Co matrix; gray blocky--R phase; light rounded block--o; Widraanstatten--R or /~; (b) Alloy S: c~-Comatrix: blocky--# phase; (c) Alloy T: 0c-Co matrix; gray--~; gray blocky--R; Widmanstatten--R. Mag. 800 ×.

The Co-Cr-W System

535

No change in amounts and morphology of the R-phase was observed after any of the heat treatments. The most conspicuous feature of the microstructure was the formation of a definite Widmanstatten structure due to a platelike precipitate. Stereographic analysis showed that the platelike phase lies parallel with the octahedral {111 } planes of the :~-Co matrix, consistent with the usual habit for TCP phases in an FCC matrix. The small size of the c~-phase decomposition product, and the narrow breadth of the platelike phase did not permit positive identification of either of these phases. The NaOH electrolyte indicated that they are probably the same phase, but did not clearly identify them as either or R phase. Alloy S precipitated more/~-phase in a {111 } Widmanstatten structure (Fig. 6b). The precipitation of R-phase sometimes occurs within agglomerated or-phase particles (Fig. 6c). R-phase also precipitated in a Widmanstatten morphology, but after 1000 min showed no tendency toward coalescence. A sample of alloy P was held at 1400c'C for 35 h and immediately quenched in water. The resulting microstructure, shown in Fig. 7, revealed that primary

Fro. 7. Alloy P after incipient melting at 1400°C. Major phase is s-Co, gray--R, lamellar--~+ cr; 200 Y. s-Co and R-phases were in equilibrium, with a small amount of liquid phase present at this temperature. The liquid phase solidified in a eutectic-like structure of small interlamellar spacing. Electron microprobe analysis did not resolve the two lamellar phases, but their average composition lay between ~ and ~ phases on the ternary diagram. Samples of alloy A, after a 1350°C anneal, were held at 800°C for 72 h. For

536

R. G. Barrows and J. B. Newkirk

both water-quenched and furnace-cooled specimens, neither decomposition nor any change in amounts of the R-phase was found. Discussion We propose that the newly-found ternary phase, having the R crystal structure, is a true, equilibrium compound in the Co-Cr-W system. It is not represented in any of the three binary systems, whereas/z and o are accepted as equilibrium phases in the Co-W and C-Cr equilibrium diagrams respectively. The experimentally determined Co-Cr-W phase diagram which we propose for 1350°C is in fair agreement with the previous work on this ternary system and with the related binary systems. The forms of the proposed/Z and (7 phase fields are similar to their respective shapes at 700°C suggested by Goldschmidt [6]. However, there is little similarity in composition and X-ray diffraction data for the newly-found R-phase and the ternary phases proposed by Drapier et ai. [8] and Lobl et al. [7]. The equilibrium temperature used for this study (1350°C) and those used by the other authors (600-1000°C and 700°C respectively) may account for this difference. The experimental results of this study are in agreement with relevant binary diagrams, except that no evidence for the existence of the 8-phase in the Co-Cr system at this temperature was found. According to a currently accepted Co-Cr phase diagram [3] alloy E should have formed this phase after having been annealed at 1350°C. On the contrary all X-ray diffraction lines given by this specimen could be indexed to the sigma-structure. The very limited amount of work performed to obtain information about the temperature stability of the R-phase furnished only tentative results. The microstructure of alloy P, Fig. 7, indicated that the R and a-Co phases are stable up to the solidus temperature of the alloy. A ternary Class II reaction, R + L ¢°°""g x + o, at approximately 1400°C could account for the liquid freezing to an ~ + o lamellar structure. Subject to future confirmation, the results of heat treating alloys R and T at 1200°C for times up to 1000 min indicated that the R-phase is stable at this temperature and in equilibrium with a-Co. Alloy R, which, after equilibrating at 1350°C, consisted of the ~ + R + c r phases, was apparently in the process of decomposing to ~ + R phases at 1200°C. The time sequence of precipitation in alloy T at 1200°C was: ~ - 4 ~ + a --~ ~ + o + R , as shown by micrographic examinations. Taken together, the results from alloys R and T show that the a + R phase field shifts to higher chromium concentration with decreasing temperature. The a-Co phase field enlarges with increasing temperature, i.e. the a-Co solvus surface slopes away from the Co corner with increasing temperature, making possible the precipitation of/z, R, or ~r phases in an ~-Co matrix by cooling. The experimental results of this study have been incorporated in a previously published tungsten-centered polar phase diagram [17], Fig. 8(a). The /z-phase _____-*

The Co-Cr-W System

537

NI

¥

(066)

(56SI

(b) {

61

{5.66}

(c) FIc. 8. Polar phase diagrams showing (a) tungsten-centered and (b) molybdenumcentered and (c) chromium-centered configurations with the first long period elements plotted around the periphery [17]; The R-phase fields and the expanded o-phase field were added by the present authors. 38

538

R. G. Barrows and J. B. Newkirk

composition range in the Co-Cr-W system agrees with the phase field shown in the published tungsten-centered diagram, but the a-phase field has been expanded somewhat in Fig. 8(a) to include the Co-Cr-W composition ranges which were experimentally determined. An R-phase field was also added to the tungstencentered diagram where it occurs in the same vicinity as the R-phase field in the molybdenum-centered polar phase diagram shown in Fig. 8(b). The composition ranges for the molybdenum R-phase field were taken from published binary and ternary transition element diagrams [16, 18, 19]. Similar phases in the chromium-, molybdenum- and tungsten-centered polar phase diagrams occur in similar composition ranges, producing a sequence of like-phase occurrences in the order: chromium, molybdenum and tungsten. The molybdenum-centered polar phase diagram contains all of the TCP phases that are contained in the chromium and tungsten diagrams, but the reverse is not always true. For example, an extended a-phase occurs only in the chromium and molybdenum diagrams, whereas the Laves, # and R phases occur only in the molybdenum and tungsten diagrams. Thus, when alloyed with B-elements of the first long period, molybdenum behaves as though it were intermediate between chromium and tungsten with respect to TCP phase occurrence. Also the FCC phase field decreases in area in the sequence of chromium, molybdenum and tungsten. This regularity suggests that mentally stacking the polar phase diagrams in the above order would furnish a useful means of visualizing phase occurrences when combinations of A-elements (for a given periodic table group number such as Cr, Mo, and W) are alloyed with combinations of B-elements (from a given long period such as Fe, Co, and Ni). We have used this concept in the formulation of a model to predict the FCC solid solution phase boundary in multi-component, transition-element superalloys [20]. Relative atomic sizes may also affect the occurrence of TCP phases in the Co-Cr-W system. Cobalt and chromium atoms are approximately the same size, whereas the tungsten atom is considerably larger. An imaginary line, drawn for a 55 a/o Co--45 a/o Cr composition on the Co-Cr side of the ternary diagram plotted in atomic percentages [Fig. 9] to the tungsten corner, intersects the TCP phases in the order a, R, and/~. If this order of TCP structure occurrence were controlled by atomic size effects, then the percentage of large CN-15 and -16 atom sites associated with each structure (Table 9) should increase with increasing tungsten content. Table 9 shows that for the sequence of a, R, and /~ the total number of CN-15 and CN-16 sites increases for these structures [21], and the tungsten content in these phases increases in the same order. Ternary compositions having a constant cobalt content of 45 a/o define a line of constant electron concentration per atom (e/a) equal to 7.35 (where e/a of chromium and tungsten is 6 and e/a of cobalt is 9). This constant e/a line also traverses the TCP phase regions in the order a, R, and/~ with increasing tungsten content. According to ideas expressed by Das and Beck [22], electron concentration does not

The Co-Cr-W System

539

appear to be a strong factor in determining the order of TCP-phase occurrence in the C o - C r - W system. Considering the/*-phase by itself, if this were purely a size compound, additions of chromium to C o - W alloys should result in the t*field projecting into the ternary diagram in a direction parallel to the C o - C r binary side of the diagram. On the other hand, if the F-phase were purely' an electron compound, the field should project parallel to the C r - W binary side. The boundary of the F-phase field given in Fig. 9 needs further verification on the tungsten-rich side. However, the trend of the cobalt-rich boundary, as

W /~,~

1350"C

/

F~\ \\ I ~ \,

//

iF

rr

<

,

, ~ . . . _ -u.

/

//

xxx

,

.

~

~

\,

~ \

\

',

.6 ,' /

\

BCC-C~

Co

CR ~TOMIC %

FIG. 9.

Isothermal section of the Co-Cr-\~: phase diagram at 1350C in atomic %.

TABLE 9 Tungsten Concentrationand High CoordinationSites~re, R, and >Phases

Structure

R

Approximate Tungsten Content (a/o)

CN-15

12

13

0

30 36

11 15

15 15

Percentage of Sites with CN-16 CN-15-,~ CN-16 13 26 30

540

R. G. Barrows and J. B. Newkirk

drawn in the figure, implies that an intermediate situation exists which somewhat favors the "size compound" correlation. That is, chromium atoms appear to be substituting primarily for the similar size cobalt atoms in the /z structure.

Summary and Conclusions A topologically close-packed phase that is isomorphous with the R-phase in the C o - C r - M o system has been found at 1350°C in the C o - C r - W system. The composition range of this phase is small and contains the elements in the approximate ratio Co23CrlsWlg. The C o - C r - W R-phase can be made to precipitate in an 0~-cobah matrix of suitable composition by the usual two-stage heat treatment; viz: by solution treating followed by a lower temperature aging treatment. The R-phase is metallographically similar to the /z and a phases which may coexist in equilibrium with it under suitable conditions of temperature and composition. On the other hand the R, the e, and the /x phases are readily distinguished from one another by potentiostatically controlled electrolytic etching. Considerations of electron concentration and atomic size effect for the stability of these T C P phases with C o - C r - W system lead to the conclusion that their occurrence is more strongly influenced by atom sizes than by electron concentration. This work was supported by a research grant from the Engineering Division of the National Science Foundation and was performed at the University of Denver. Accepted September 11, 1972

References 1. R. G. Barrows and J. B. Newkirk, Proc. 2nd lnt. Conf. on Strength of Metals and Alloys, Vol. III (1970), p. 1047. 2. J. B. Darby Jr. and P. A. Beck, Trans. A I M E 212, 235 (1958). 3. M. Hansen and P. Anderko, Constitution of Binary Alloys, McGraw-Hill, New York (1958). 4. H. J. Beattie, Jr. and W. C. Hagel, Trans. AIME 233, 277 (1965). 5. W. K6ster, Z. Metallk. 25, 22 (1933). 6. H. J. Goldschmidt, J. Less-Common Metals, 2, 138 (1960). 7. K. Lobl, H. Tuma, and J. Vodsedalek, Journess Internationales des Applications du Cobalt, Brussels (1965), p. 269. 8. J. M. Drapier and D. Coutsouradis, Cobalt, No. 39 (1968), p. 63. 9. J. D. Jones and W. Hume-Rothery, J. 1ton Steel lnst. 204, 1 (1966). 10. J. E. Hilliard, Quantitative Microscopy, (R. T. DeHoff and F. N. Rhines, Eds.), McGraw-Hill, New York (1968), Chap. 3.

The C o - C r - W System

541

11. A. C. Larson, R. B. Roof, and D. T. Cromer, An integrated series of crystallographic computer programs, X, anisotropic structure factor calculation and powder pattern generation, Los Alamos Scientific Laboratory Report L.4-3335, Los Alamos, New Mexico (1965). 12. W. B. Pearson, A Handbook of Lattice Spacings and Str,ct,res of .'lletals and Alloys-I'olume 2, Pergamon Press (1967). 13. Y. Komura, W. G. Sly, and D. P. Shoemaker, .4cta Cryst. 13, 575 (1960). 14. J. \¥. Colby, Magic--A Computer Program .for Quantitative Electron Microprobe Analysis, Bell Telephone Laboratories, Inc., Allentown, Pa. 15. F. N. Rhines, Phase Diagrams in Metallurgy, McGraw-Hill, New York (1956). 16. S. Rideout, W. D. Manly, E. L. Kamen, B. S. Lement, and P. A. Beck, Trans. ~4IME 191, 872 (1951). 17. C. T. Sims, The Role of Refractory" Metals in Austenitic Snperalloys, 6th Plansee Seminar, Reutte, Austria (June 1968). 18. A. K. Sinha, R. A. Buckley, and W. Hume-Rothery, J. of the Iron and Steel Institute 191 (1967). 19. M. V. Nevitt, Alloy chemistry of transition element, in Electronic Struct,re and Alloy Chemistry of the Transition Elements (P. A. Beck, Ed.) Interscience, New York (1963), p. 101. 20. 'Fo be published in Metallurgical Transactions, 1972 or 1973. 21. C. B. Shoemaker and D. P. Shoemaker, Structural properties of some o-phase related phases, in Developments in the Struct,ral Chemistry of .4lloy Phases (B. C. Giessen, Ed.), Plenum Press, New York (1969), p. 107. 22. B. N. Das and P. A. Beck, Trans. AIME 218, 733 (1960).