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Plating on Invar, VascoMax C-200, and 440C stainless steel
11¢R
mA/INBS ELSEVIER
Surface a n d C o a t i n g s T e c h n o l o g y 78 (1996) 14-18
Plating on Invar, VascoMax C-200, and 440C stainless steel J.W. Dini Lawrence Livermore National Laboratory, Livermore, CA 94551, USA
Received 24 March 1994; accepted in final form 22 September 1994
Abstract
Procedures for plating on Invar, VascoMax C-200 and 440C stainless steel were evaluated quantitatively for adhesion by use of ring shear and I-beam tests. The ring shear tests involve forcing a rod with premachined rings of thick electrodeposit through a hardened steel die having a hole with a diameter greater than that of the rod but less than that of the rod plus coating. The I-beam tests provide a method for testing adhesion in a tensile fashion and simulate conditions some of the plated parts would see in service. Results with Invar revealed acceptable adhesion with a process that included a Wood's nickel strike. Higher adhesion values were obtained with VascoMax C-200 with use of anodic treatment in phosphoric acid followed by cathodic treatment in sulfuric acid or anodic treatment in sulfuric acid followed by a Wood's nickel strike, Similarly, highest adhesion values were obtained with 440C stainless steel when anodic treatment in sulfuric acid and Wood's nickel striking were used. Keywords: Electroplating;
Adhesion; S h e a r tests; Tensile test; Nickel plating
I-beam tests were used to provide quantitative measures of bond strength.
1. Introduction
The purpose of this paper is to present quantitative adhesion data for deposits plated on Invar, VascoMax C-200 maraging steel and 440C stainless steel. These alloys have high amounts of either nickel or chromium and a variety of other alloying elements (Table 1), thus necessitating special treatment to ensure good adhesion when they are coated via electroplating. Ring shear and
Table 1 C o m p o s i t i o n of alloys Element
Invar
V a s c o M a x C-200
440C Stainless Steel
Ni Cr Co Mo T AI Si Mn C S P Zr B Fe
36.0 -----0.30 0.35 0.12 ----Balance
18.5 -8.5 3.250 0.20 0.10 0.10 0.10 0.03 0.01 0.01 0.0l 0.003 Balance
-17.0 -0.75
Elsevier Science S.A. SSDI 0 2 5 7 - 8 9 7 2 ( 9 4 ) 0 2 3 8 4 - 0
-1.0 1.0 1.1 0.03 0.04 -Balance
1.1. Invar
Invar is a binary alloy of iron and nickel (64% iron, 36% nickel and minor amounts of manganese, silicon and carbon). Its coefficient of thermal expansion is so low that its length is almost invariable for ordinary changes of temperature. For this reason Guillaume gave the alloy the name "Invar" [ 1 ]. Specially treated Invar sheets have exhibited thermal expansion coefficients of 10-8 oC 1; however, values of 0.2× 1 0 . 6 ° C - Z - 2 x 10 6 °C t are more typical of commercial alloys [ 2 - 4 ] . Other alloys of this family include Super Invar (a ternary alloy containing 64% iron, 31% nickel, and 5% cobalt) which exhibits a thermal expansion coefficient even lower than Invar and Stainless Invar (a ternary alloy containing 37% iron, 54% cobalt and 9% chromium) which combines a low thermal expansion coefficient with good corrosion resistance [3]. Invar alloys are used for absolute standards of length, rods and tapes for geodetic work, compensating pendulums and balance wheels in clocks and watches, elements in moving parts where control of expansion is necessary as in certain internal combustion engine pistons, bimetal strips, glassto-metal seals, and thermostatic strips. Recent applications include microwave guides, laser housings, optical
J. W. Dini/Surface and Coatings Technology 78 (1996) 14-18
assemblies for imaging instruments on Viking and Voyager spacecraft, as possible construction materials for optical mirrors in space applications, and liquid natural gas containers in tankers and printed circuit board cores [3]. Our interest at L L N L was directed at coating Invar with nickel and electroless nickel deposits which could be subsequently optically polished or diamond turned to produce mirror surfaces for optics applications. Recommended procedures for plating on Invar include anodic treatment in sulfuric acid solution [5] or anodic and then cathodic treatment in Wood's [-6] nickel strike solution, or cathodic treatment in Wood's nickel strike solution [7]. The Wood's strike, which contains 240 g nickel chloride 1-1 and 125 ml hydrochloric acid 1 1, is used as a base for subsequent coatings. 1.2. VascoMax C-200
VascoMax alloys (18% nickel maraging steels) are divided into two broad classes depending on the primary strengthening element used in the material, cobalt or titanium [8]. Their structural properties provide substantial toughness together with high ultimate tensile strengths, varying from 1450 M P a for C-200 alloys to 2415 MPa for C-350 alloys. Applications have included solid propellant rocket motor cases, load cells, helicopter drive shafts, aircraft wing components, torsion bars on the Apollo 15 Lunar Roving Vehicle (the first wheeled vehicle on the moon), and critical components for the space shuttle Columbia [8]. Our interest in VascoMax C-200 was in using electroplated nickel to close over channels for a NASA combustor facility. This process consisted of plating thick nickel over wax-filled channels and their accompanying lands and then removing the wax to open the channels. Earlier work had shown this approach to work effectively with 405 stainless steel [9]. Recommended procedures for plating on maraging steels typically include anodic treatment in sulfuric acid solution followed by Wood's nickel striking [-8,10-13].
15
then cathodic treatment in highly acidic solutions. Anodic treatment in sulfuric acid solution followed by Wood's nickel striking has been shown to be very effective for a variety of stainless steel alloys [ 17,18].
2. Experimental details Ring shear and/or I-beam tension tests were used to obtain quantitative adhesion data for all processes evaluated. Since both of these tests have been described in detail previously [19,20], they will be covered only briefly here. 2.1. Ring shear tests
A cylindrical rod is cleaned, activated, and plated with a minimum thickness of 1.5 ram. The rod is machined in a manner that removes the electrodeposit except for small rings of predetermined width (generally 1.5 mm wide). The rod is then cut between the plated rings. Sections with plated rings are tested by forcing the rod through a hardened steel die having a hole with a diameter greater than that of the rod but less than that of the rod plus the coating. Fig. 1 shows a cross-section of a ring shear specimen and test die. The test specimen and die are designed to allow failure during testing to occur in a variety of locations: at the interface between the substrate and coating, in the substrate, in the coating, or in a mixed mode fashion. After testing, the failures are examined either visually or metallographically. When adhesion is poor, the deposit separates from the substrate at the interface; when adhesion is optimum, separation occurs within either the deposit or substrate, depending on which component has the lowest shear strength. A mixed mode failure consisting of partial failure at the interface and partial failure in the deposit provides adhesion between the two extremes of poor and optimum. For these situations, adhesion is assessed by comparing the shear strengths of the deposit and the substrate with those obtained with the test specimens.
1.3. Stainless steel 440C 2.2. I-beam tests
This alloy, which is of the martensitic stainless steel family, is capable of being age hardened to high strengths, e.g. ultimate tensile strengths of 1970 M P a [14]. It also exhibits the highest hardness (RB 97) of hardenable stainless steels used for ball bearing applications [ 15 ]. The material was evaluated in the as-received condition and after heat treating to provide maximum hardness. Many procedures have been recommended for activating stainless steels for electroplating [ 16]. They include immersion in acids with simultaneous activation-plating treatments such as a Wood's nickel strike, anodic treatments in various solutions, and a combination of anodic
I-beam tests were used as a supplementary evaluation technique for the VascoMax C-200 since these tests simulate the conditions that plated parts would see in service. I-beam tests provide a method for testing a deposit-substrate combination in a tensile fashion. Parallel grooves 6.4mm wide by 6.4mm deep and spaced 1.57 mm apart are machined on one side of a 152 mm by 152 mm by 12.7 mm substrate. Aluminum strips 0.81 mm thick are then wedged into the grooves. The substrate is cleaned, plated with a minimum of 2.54 mm of deposit, and then machined to produce the I-beam specimens from which the aluminum is dissolved.
16
J. W. Dini/Surface and Coatings Technology 78 (1996) 14-18
SPECIMEN UNDER TEST (CUT AWAY VIEW)
12.4 DIA 15.9 ~E ~ DIA
I 25.4 ~'5.1
_ I -P~--
(ALL DIMENSIONS ARE IN ram)
[]
i
10.2 ~
I.
12.7 19.0 1.60 1.65
Fig. 1. Design for a test specimen and die which can be used to measure adhesion in a shear mode.
Fig. 2 shows an I-beam specimen. Testing is done on a standard tension testing machine.
3. Results
The results are presented in Tables 2 and 3. The ring shear data of Table 2 reveal that a bond strength of 284 M P a was obtained with Invar. This is fairly good adhesion and represents a mixed mode failure: partially in the coating and partially at the interface between the coating and substrate. Since the shear strengths of Invar (417MPa) and the nickel sulfamate electrodeposit (500 MPa), are higher than the 284 M P a obtained in these tests, it is evident that higher adhesion values are obtainable. If higher adhesion is required, use of an anodic sulfuric acid treatment prior to Wood's nickel striking would probably work. We avoided this step because it can roughen the substrate surface and we were not allowed to do this to the Invar for our applications since we were dealing with optical surfaces. Ring shear data for the VascoMax C-200 alloy show good bonds regardless of which of the two processes were used: anodic in phosphoric acid followed by cathodic in sulfuric acid (486 MPa) or anodic in sulfuric acid, a chromic acid pickle and then Wood's nickel striking (453 MPa). However, when these bonds were tested in a tensile fashion (Table 3), the former process provided considerably inferior adhesion (121 vs. 432 MPa). This is probably because the anodic sulfuric
I I I I a I I
I I I I I I I
I I
I I
I I
I I
12.7mm
TOP VIEW
PLATING 2.5ramTHICK
6.4ram MINIMUM
1. SIT) rrl -~.-,~m=
~
SUBSTRATE
FRONTVIEW Fig. 2. I-beam test specimen which allows for evaluating adhesion in tensile fashion.
J. W. Dini/Surface and Coatings Technology 78 (1996) 14 18
17
Table 2 Ring shear data for plated Invar, VascoMax C-200, and 440C stainless steel Substrate
Activating procedure a
Shear strength b (MPa)
Invar
Wood's nickel strike~, anodic 3 rain at 2140 A m -z, anodic desmut for 2 min at 2140 A m -z in a non-phosphate based cleaner at 22 °C, immerse in nitric acid (71% by volume) for 10 s at 22 °C, electroless nickel plate 25 gm thick d, nickel sulfamate plate e to final thickness Phosphoric acid (70-75 vol.%), anodic 1 min at 22 °C and 1605 A m -z, sulfuric acid (25% by weight) cathodic 1 min at 22 °C and 1070 A m -z, nickel sulfamate plate Sulfuric acid (25% by weight) anodic 2 min at 22 °C and 2140 A m -z, immerse in 45 g chromic acid 1 ~ and 20 ml sulfuric acid 1-1 for 1 min at 22 °C, Wood's nickel strike cathodic for 1 min at 321 A m -z, nickel sulfamate plate Wood's nickel, cathodic 5 min at 268 A m -z, nickel sulfamate plate
284
11
486
29
453
22
267
87
Wood's nickel, cathodic 5 rain at 268 A m 2 nickel sulfamate plate
299
133
Sulfuric Wood's Sulfuric Wood's
387
7
497
47
VascoMax C-200 VascoMax C-200
440C (as received) 440C f (heat treated) 440C (as received) 440C f (heat treated)
acid (70% by weight) anodic 5 min at 22 °C and 1070 A m 2, nickel cathodic 5 rain at 268 A m -z, nickel sulfamate plate acid (70% by weight) anodic 5 min at 22 °C and 1070 A m -z, nickel cathodic 5 min at 268 A m -z, nickel sulfamate plate
Standard deviation
a A standard preliminary cleaning procedure on all rods prior to the activation procedure consisted of cathodic and anodic alkaline cleaning followed by pickling in hydrochloric acid (18% by weight). b Average of at least five tests. ° The Wood's nickel strike solution contained 240 g nickel chloride hexahydrate 1 1 and 125 ml hydrochloric acid 1-1 (37 wt,%). d Electroless nickel was deposited in a proprietary solution operated at 90 °C. The deposit contained 13 wt.% phosphorus. ° The nickel sulfamate solution contained 450 g nickel sulfamate 1-1, I g nickel chloride 1 1, 40 g boric acid 1- a and was operated at a pH of 4.0, temperature of 50 °C, and current density of 270 A m -z. f The hardening process consisted of heating at 1025 °C, oil quenching, and then tempering at 565 °C. All of this was done prior to electroplating. Table 3 I-beam test data for VascoMax C-200 Activation process
I-beam tensile strength (MPa)
Standard deviation
Phosphoric acid (70-75 vol.%), anodic 1 min at 22 °C and 1605 A m -z, sulfuric acid (25 wt.%), cathodic 1 min at 22 °C and 1070 A m -a, nickel sulfamate plate Sulfuric acid (25 wt.%), anodic 2 min at 22 °C and 2140 A m -2, immerse in 45 g chromic acid 1 i and 20 g sulfuric acid 1 ~ for 1 min at 22 °C, Wood's nickel cathodic for 1 rain at 321 A m 2, nickel sulfamate plate
121
23
432
42
Average of at least five tests. a c i d t r e a t m e n t r o u g h e n s the surface a n d p r o v i d e s sites for m e c h a n i c a l i n t e r l o c k i n g o f the deposit. C l e a r l y , to o b t a i n o p t i m u m a d h e s i o n , a c o m b i n a t i o n of a n o d i c t r e a t m e n t in sulfuric a c i d f o l l o w e d b y W o o d ' s nickel s t r i k i n g is n e e d e d . S i m i l a r to the V a s c o M a x alloy, use of a n o d i c t r e a t m e n t
in sulfuric a c i d f o l l o w e d by W o o d ' s nickel s t r i k i n g p r o v i d e d t h e h i g h e s t a d h e s i o n v a l u e s w i t h the 4 4 0 C stainless steel specimens. U s e of a W o o d ' s nickel strike w i t h n o p r i o r a n o d i c t r e a t m e n t in sulfuric a c i d p r o v i d e d reduced ring shear adhesion values with data that were h i g h l y v a r i a b l e as n o t e d by t h e s t a n d a r d d e v i a t i o n s . T h e observation of higher bond strengths with a combined p r o c e s s i n c l u d i n g a n o d i c t r e a t m e n t in sulfuric a c i d solut i o n f o l l o w e d b y W o o d ' s nickel s t r i k i n g has also b e e n n o t e d for a n o t h e r m a r a g i n g steel [ 13], a n d A M 363 a n d 21-6-9 stainless steels [ 1 7 ] . W h e n t h e 4 4 0 C s u b s t r a t e s w e r e t e m p e r e d p r i o r to e l e c t r o p l a t i n g to i n c r e a s e t h e i r s t r e n g t h , p l a t e d b o n d s t r e n g t h s also i n c r e a s e d ( T a b l e 2).
4. Summary Q u a n t i t a t i v e r i n g s h e a r a d h e s i o n tests for a c t i v a t i n g p r o c e d u r e s for p r e p a r i n g I n v a r , V a s c o M a x C - 2 0 0 a n d 44i;C stainless steel for p l a t i n g s h o w e d the i m p o r t a n c e of u s i n g a n a n o d i c t r e a t m e n t in sulfuric a c i d f o l l o w e d b y W o o d ' s nickel s t r i k i n g in p r o v i d i n g o p t i m u m a d h e sion. A n a d d i t i o n a l test ( I - b e a m ) was u s e d w i t h the V a s c o M a x a l l o y to e v a l u a t e f u r t h e r a d h e s i o n in a m a n n e r d u p l i c a t i n g t h a t seen in h a r d w a r e for the i n t e n d e d a p p l i c a t i o n . T h i s test was e v e n m o r e d i s c r i m i -
18
J.W. Dini/Surface and Coatings Technology 78 (1996) 14-18
nating in showing the importance of the sulfuric acid anodic treatment step prior to Wood's nickel striking. All these data show that excellent adhesion can be obtained on Invar, VascoMax C-200 and 440C stainless steel. Also, the value of utilizing a test that closely duplicates conditions that will be seen with the end product was clearly demonstrated.
Acknowledgment This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract W-704-Eng-48.
References [ 1] T. Lyman (ed.), Metals Handbook, Vol. 1, Properties and Selection of Metals, ASM, 8th edn., 1961. [2] Expansion Alloys, Bull. CEA-01 (Magnetics Division of Spang Industries, San Jose, CA). [3] D.L. Grimmett, M. Schwartz and K. Nobe, Plat. Surf. Finish., 75 (June 1988) 94.
[-4] C.W. Marshall, Nat. SAMPE Symp. and Exhibition, Vol. 21, 1976, p. 261. [5] W.W. Sellers and C.B. Sanborn, Proc. Am. Electroplaters' Soc., 44, (1957) 36. [6] D. Wood, Met. Ind., 36 (1938) 330. E7] I. Rajagopal, K.S. Rajam and S.R. Rajagopalan, Met. Finish., 90, (April 1992) 33. [8] VascoMax C-200, C-250, C-300, C-350, Teledyne Vasco, Paramount, CA, 1982. [9] J.W. Dini and H.R. Johnson, Plat. Surf. Finish., 64 (August 1977) 44. [10] G.A. DiBari, Plating, 52 (1965) 1157. Ell] G.A. DiBari, US Patent 3,338,803, August 1967. [12] J.P. Young, V.A. Lamb, G.I. Reid, J.R. Berkeley and W. Ng, Plating, 57, (1970) 921. [13] J.W. Dini and H.R. Johnson, Met. Finish., 72 (August 1974) 44. [14] Materials selector 1991, Mater. Eng., (December 1990) 49. [15] Met. Prog., 106 (1) (1974) 51. [16] Preparation of and plating on stainless steel, ASTM B 254-70 (ASTM, Philadelphia, PA). [17] J.W. Dini, H.R. Johnson and R.S. Jacobson, in R. Sard, H. Leidheiser, Jr., and F. Ogburn (eds.), Properties of Electrodeposits, Their Measurement and Significance, Electrochemical Society, Pennington, NJ, 1975, pp. 307 318. [18] J.W. Dini and H.R. Johnson, Plat. Surf. Finish., 69 (November 1982) 63. [19] J.W. Dini and H.R. Johnson, Met. Finish., 75 (March 1977) 42; 75 (April 1977) 48. [203 J.W. Dini and H.R. Johnson, in K.L. Mittal (ed.), Adhesion Measurement of Thin Films, Thick Films, and Bulk Coatings, ASTM 640 1978, pp. 305-326 (ASTM, Philadelphia, PA).
mA/INBS ELSEVIER
Surface a n d C o a t i n g s T e c h n o l o g y 78 (1996) 14-18
Plating on Invar, VascoMax C-200, and 440C stainless steel J.W. Dini Lawrence Livermore National Laboratory, Livermore, CA 94551, USA
Received 24 March 1994; accepted in final form 22 September 1994
Abstract
Procedures for plating on Invar, VascoMax C-200 and 440C stainless steel were evaluated quantitatively for adhesion by use of ring shear and I-beam tests. The ring shear tests involve forcing a rod with premachined rings of thick electrodeposit through a hardened steel die having a hole with a diameter greater than that of the rod but less than that of the rod plus coating. The I-beam tests provide a method for testing adhesion in a tensile fashion and simulate conditions some of the plated parts would see in service. Results with Invar revealed acceptable adhesion with a process that included a Wood's nickel strike. Higher adhesion values were obtained with VascoMax C-200 with use of anodic treatment in phosphoric acid followed by cathodic treatment in sulfuric acid or anodic treatment in sulfuric acid followed by a Wood's nickel strike, Similarly, highest adhesion values were obtained with 440C stainless steel when anodic treatment in sulfuric acid and Wood's nickel striking were used. Keywords: Electroplating;
Adhesion; S h e a r tests; Tensile test; Nickel plating
I-beam tests were used to provide quantitative measures of bond strength.
1. Introduction
The purpose of this paper is to present quantitative adhesion data for deposits plated on Invar, VascoMax C-200 maraging steel and 440C stainless steel. These alloys have high amounts of either nickel or chromium and a variety of other alloying elements (Table 1), thus necessitating special treatment to ensure good adhesion when they are coated via electroplating. Ring shear and
Table 1 C o m p o s i t i o n of alloys Element
Invar
V a s c o M a x C-200
440C Stainless Steel
Ni Cr Co Mo T AI Si Mn C S P Zr B Fe
36.0 -----0.30 0.35 0.12 ----Balance
18.5 -8.5 3.250 0.20 0.10 0.10 0.10 0.03 0.01 0.01 0.0l 0.003 Balance
-17.0 -0.75
Elsevier Science S.A. SSDI 0 2 5 7 - 8 9 7 2 ( 9 4 ) 0 2 3 8 4 - 0
-1.0 1.0 1.1 0.03 0.04 -Balance
1.1. Invar
Invar is a binary alloy of iron and nickel (64% iron, 36% nickel and minor amounts of manganese, silicon and carbon). Its coefficient of thermal expansion is so low that its length is almost invariable for ordinary changes of temperature. For this reason Guillaume gave the alloy the name "Invar" [ 1 ]. Specially treated Invar sheets have exhibited thermal expansion coefficients of 10-8 oC 1; however, values of 0.2× 1 0 . 6 ° C - Z - 2 x 10 6 °C t are more typical of commercial alloys [ 2 - 4 ] . Other alloys of this family include Super Invar (a ternary alloy containing 64% iron, 31% nickel, and 5% cobalt) which exhibits a thermal expansion coefficient even lower than Invar and Stainless Invar (a ternary alloy containing 37% iron, 54% cobalt and 9% chromium) which combines a low thermal expansion coefficient with good corrosion resistance [3]. Invar alloys are used for absolute standards of length, rods and tapes for geodetic work, compensating pendulums and balance wheels in clocks and watches, elements in moving parts where control of expansion is necessary as in certain internal combustion engine pistons, bimetal strips, glassto-metal seals, and thermostatic strips. Recent applications include microwave guides, laser housings, optical
J. W. Dini/Surface and Coatings Technology 78 (1996) 14-18
assemblies for imaging instruments on Viking and Voyager spacecraft, as possible construction materials for optical mirrors in space applications, and liquid natural gas containers in tankers and printed circuit board cores [3]. Our interest at L L N L was directed at coating Invar with nickel and electroless nickel deposits which could be subsequently optically polished or diamond turned to produce mirror surfaces for optics applications. Recommended procedures for plating on Invar include anodic treatment in sulfuric acid solution [5] or anodic and then cathodic treatment in Wood's [-6] nickel strike solution, or cathodic treatment in Wood's nickel strike solution [7]. The Wood's strike, which contains 240 g nickel chloride 1-1 and 125 ml hydrochloric acid 1 1, is used as a base for subsequent coatings. 1.2. VascoMax C-200
VascoMax alloys (18% nickel maraging steels) are divided into two broad classes depending on the primary strengthening element used in the material, cobalt or titanium [8]. Their structural properties provide substantial toughness together with high ultimate tensile strengths, varying from 1450 M P a for C-200 alloys to 2415 MPa for C-350 alloys. Applications have included solid propellant rocket motor cases, load cells, helicopter drive shafts, aircraft wing components, torsion bars on the Apollo 15 Lunar Roving Vehicle (the first wheeled vehicle on the moon), and critical components for the space shuttle Columbia [8]. Our interest in VascoMax C-200 was in using electroplated nickel to close over channels for a NASA combustor facility. This process consisted of plating thick nickel over wax-filled channels and their accompanying lands and then removing the wax to open the channels. Earlier work had shown this approach to work effectively with 405 stainless steel [9]. Recommended procedures for plating on maraging steels typically include anodic treatment in sulfuric acid solution followed by Wood's nickel striking [-8,10-13].
15
then cathodic treatment in highly acidic solutions. Anodic treatment in sulfuric acid solution followed by Wood's nickel striking has been shown to be very effective for a variety of stainless steel alloys [ 17,18].
2. Experimental details Ring shear and/or I-beam tension tests were used to obtain quantitative adhesion data for all processes evaluated. Since both of these tests have been described in detail previously [19,20], they will be covered only briefly here. 2.1. Ring shear tests
A cylindrical rod is cleaned, activated, and plated with a minimum thickness of 1.5 ram. The rod is machined in a manner that removes the electrodeposit except for small rings of predetermined width (generally 1.5 mm wide). The rod is then cut between the plated rings. Sections with plated rings are tested by forcing the rod through a hardened steel die having a hole with a diameter greater than that of the rod but less than that of the rod plus the coating. Fig. 1 shows a cross-section of a ring shear specimen and test die. The test specimen and die are designed to allow failure during testing to occur in a variety of locations: at the interface between the substrate and coating, in the substrate, in the coating, or in a mixed mode fashion. After testing, the failures are examined either visually or metallographically. When adhesion is poor, the deposit separates from the substrate at the interface; when adhesion is optimum, separation occurs within either the deposit or substrate, depending on which component has the lowest shear strength. A mixed mode failure consisting of partial failure at the interface and partial failure in the deposit provides adhesion between the two extremes of poor and optimum. For these situations, adhesion is assessed by comparing the shear strengths of the deposit and the substrate with those obtained with the test specimens.
1.3. Stainless steel 440C 2.2. I-beam tests
This alloy, which is of the martensitic stainless steel family, is capable of being age hardened to high strengths, e.g. ultimate tensile strengths of 1970 M P a [14]. It also exhibits the highest hardness (RB 97) of hardenable stainless steels used for ball bearing applications [ 15 ]. The material was evaluated in the as-received condition and after heat treating to provide maximum hardness. Many procedures have been recommended for activating stainless steels for electroplating [ 16]. They include immersion in acids with simultaneous activation-plating treatments such as a Wood's nickel strike, anodic treatments in various solutions, and a combination of anodic
I-beam tests were used as a supplementary evaluation technique for the VascoMax C-200 since these tests simulate the conditions that plated parts would see in service. I-beam tests provide a method for testing a deposit-substrate combination in a tensile fashion. Parallel grooves 6.4mm wide by 6.4mm deep and spaced 1.57 mm apart are machined on one side of a 152 mm by 152 mm by 12.7 mm substrate. Aluminum strips 0.81 mm thick are then wedged into the grooves. The substrate is cleaned, plated with a minimum of 2.54 mm of deposit, and then machined to produce the I-beam specimens from which the aluminum is dissolved.
16
J. W. Dini/Surface and Coatings Technology 78 (1996) 14-18
SPECIMEN UNDER TEST (CUT AWAY VIEW)
12.4 DIA 15.9 ~E ~ DIA
I 25.4 ~'5.1
_ I -P~--
(ALL DIMENSIONS ARE IN ram)
[]
i
10.2 ~
I.
12.7 19.0 1.60 1.65
Fig. 1. Design for a test specimen and die which can be used to measure adhesion in a shear mode.
Fig. 2 shows an I-beam specimen. Testing is done on a standard tension testing machine.
3. Results
The results are presented in Tables 2 and 3. The ring shear data of Table 2 reveal that a bond strength of 284 M P a was obtained with Invar. This is fairly good adhesion and represents a mixed mode failure: partially in the coating and partially at the interface between the coating and substrate. Since the shear strengths of Invar (417MPa) and the nickel sulfamate electrodeposit (500 MPa), are higher than the 284 M P a obtained in these tests, it is evident that higher adhesion values are obtainable. If higher adhesion is required, use of an anodic sulfuric acid treatment prior to Wood's nickel striking would probably work. We avoided this step because it can roughen the substrate surface and we were not allowed to do this to the Invar for our applications since we were dealing with optical surfaces. Ring shear data for the VascoMax C-200 alloy show good bonds regardless of which of the two processes were used: anodic in phosphoric acid followed by cathodic in sulfuric acid (486 MPa) or anodic in sulfuric acid, a chromic acid pickle and then Wood's nickel striking (453 MPa). However, when these bonds were tested in a tensile fashion (Table 3), the former process provided considerably inferior adhesion (121 vs. 432 MPa). This is probably because the anodic sulfuric
I I I I a I I
I I I I I I I
I I
I I
I I
I I
12.7mm
TOP VIEW
PLATING 2.5ramTHICK
6.4ram MINIMUM
1. SIT) rrl -~.-,~m=
~
SUBSTRATE
FRONTVIEW Fig. 2. I-beam test specimen which allows for evaluating adhesion in tensile fashion.
J. W. Dini/Surface and Coatings Technology 78 (1996) 14 18
17
Table 2 Ring shear data for plated Invar, VascoMax C-200, and 440C stainless steel Substrate
Activating procedure a
Shear strength b (MPa)
Invar
Wood's nickel strike~, anodic 3 rain at 2140 A m -z, anodic desmut for 2 min at 2140 A m -z in a non-phosphate based cleaner at 22 °C, immerse in nitric acid (71% by volume) for 10 s at 22 °C, electroless nickel plate 25 gm thick d, nickel sulfamate plate e to final thickness Phosphoric acid (70-75 vol.%), anodic 1 min at 22 °C and 1605 A m -z, sulfuric acid (25% by weight) cathodic 1 min at 22 °C and 1070 A m -z, nickel sulfamate plate Sulfuric acid (25% by weight) anodic 2 min at 22 °C and 2140 A m -z, immerse in 45 g chromic acid 1 ~ and 20 ml sulfuric acid 1-1 for 1 min at 22 °C, Wood's nickel strike cathodic for 1 min at 321 A m -z, nickel sulfamate plate Wood's nickel, cathodic 5 min at 268 A m -z, nickel sulfamate plate
284
11
486
29
453
22
267
87
Wood's nickel, cathodic 5 rain at 268 A m 2 nickel sulfamate plate
299
133
Sulfuric Wood's Sulfuric Wood's
387
7
497
47
VascoMax C-200 VascoMax C-200
440C (as received) 440C f (heat treated) 440C (as received) 440C f (heat treated)
acid (70% by weight) anodic 5 min at 22 °C and 1070 A m 2, nickel cathodic 5 rain at 268 A m -z, nickel sulfamate plate acid (70% by weight) anodic 5 min at 22 °C and 1070 A m -z, nickel cathodic 5 min at 268 A m -z, nickel sulfamate plate
Standard deviation
a A standard preliminary cleaning procedure on all rods prior to the activation procedure consisted of cathodic and anodic alkaline cleaning followed by pickling in hydrochloric acid (18% by weight). b Average of at least five tests. ° The Wood's nickel strike solution contained 240 g nickel chloride hexahydrate 1 1 and 125 ml hydrochloric acid 1-1 (37 wt,%). d Electroless nickel was deposited in a proprietary solution operated at 90 °C. The deposit contained 13 wt.% phosphorus. ° The nickel sulfamate solution contained 450 g nickel sulfamate 1-1, I g nickel chloride 1 1, 40 g boric acid 1- a and was operated at a pH of 4.0, temperature of 50 °C, and current density of 270 A m -z. f The hardening process consisted of heating at 1025 °C, oil quenching, and then tempering at 565 °C. All of this was done prior to electroplating. Table 3 I-beam test data for VascoMax C-200 Activation process
I-beam tensile strength (MPa)
Standard deviation
Phosphoric acid (70-75 vol.%), anodic 1 min at 22 °C and 1605 A m -z, sulfuric acid (25 wt.%), cathodic 1 min at 22 °C and 1070 A m -a, nickel sulfamate plate Sulfuric acid (25 wt.%), anodic 2 min at 22 °C and 2140 A m -2, immerse in 45 g chromic acid 1 i and 20 g sulfuric acid 1 ~ for 1 min at 22 °C, Wood's nickel cathodic for 1 rain at 321 A m 2, nickel sulfamate plate
121
23
432
42
Average of at least five tests. a c i d t r e a t m e n t r o u g h e n s the surface a n d p r o v i d e s sites for m e c h a n i c a l i n t e r l o c k i n g o f the deposit. C l e a r l y , to o b t a i n o p t i m u m a d h e s i o n , a c o m b i n a t i o n of a n o d i c t r e a t m e n t in sulfuric a c i d f o l l o w e d b y W o o d ' s nickel s t r i k i n g is n e e d e d . S i m i l a r to the V a s c o M a x alloy, use of a n o d i c t r e a t m e n t
in sulfuric a c i d f o l l o w e d by W o o d ' s nickel s t r i k i n g p r o v i d e d t h e h i g h e s t a d h e s i o n v a l u e s w i t h the 4 4 0 C stainless steel specimens. U s e of a W o o d ' s nickel strike w i t h n o p r i o r a n o d i c t r e a t m e n t in sulfuric a c i d p r o v i d e d reduced ring shear adhesion values with data that were h i g h l y v a r i a b l e as n o t e d by t h e s t a n d a r d d e v i a t i o n s . T h e observation of higher bond strengths with a combined p r o c e s s i n c l u d i n g a n o d i c t r e a t m e n t in sulfuric a c i d solut i o n f o l l o w e d b y W o o d ' s nickel s t r i k i n g has also b e e n n o t e d for a n o t h e r m a r a g i n g steel [ 13], a n d A M 363 a n d 21-6-9 stainless steels [ 1 7 ] . W h e n t h e 4 4 0 C s u b s t r a t e s w e r e t e m p e r e d p r i o r to e l e c t r o p l a t i n g to i n c r e a s e t h e i r s t r e n g t h , p l a t e d b o n d s t r e n g t h s also i n c r e a s e d ( T a b l e 2).
4. Summary Q u a n t i t a t i v e r i n g s h e a r a d h e s i o n tests for a c t i v a t i n g p r o c e d u r e s for p r e p a r i n g I n v a r , V a s c o M a x C - 2 0 0 a n d 44i;C stainless steel for p l a t i n g s h o w e d the i m p o r t a n c e of u s i n g a n a n o d i c t r e a t m e n t in sulfuric a c i d f o l l o w e d b y W o o d ' s nickel s t r i k i n g in p r o v i d i n g o p t i m u m a d h e sion. A n a d d i t i o n a l test ( I - b e a m ) was u s e d w i t h the V a s c o M a x a l l o y to e v a l u a t e f u r t h e r a d h e s i o n in a m a n n e r d u p l i c a t i n g t h a t seen in h a r d w a r e for the i n t e n d e d a p p l i c a t i o n . T h i s test was e v e n m o r e d i s c r i m i -
18
J.W. Dini/Surface and Coatings Technology 78 (1996) 14-18
nating in showing the importance of the sulfuric acid anodic treatment step prior to Wood's nickel striking. All these data show that excellent adhesion can be obtained on Invar, VascoMax C-200 and 440C stainless steel. Also, the value of utilizing a test that closely duplicates conditions that will be seen with the end product was clearly demonstrated.
Acknowledgment This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract W-704-Eng-48.
References [ 1] T. Lyman (ed.), Metals Handbook, Vol. 1, Properties and Selection of Metals, ASM, 8th edn., 1961. [2] Expansion Alloys, Bull. CEA-01 (Magnetics Division of Spang Industries, San Jose, CA). [3] D.L. Grimmett, M. Schwartz and K. Nobe, Plat. Surf. Finish., 75 (June 1988) 94.
[-4] C.W. Marshall, Nat. SAMPE Symp. and Exhibition, Vol. 21, 1976, p. 261. [5] W.W. Sellers and C.B. Sanborn, Proc. Am. Electroplaters' Soc., 44, (1957) 36. [6] D. Wood, Met. Ind., 36 (1938) 330. E7] I. Rajagopal, K.S. Rajam and S.R. Rajagopalan, Met. Finish., 90, (April 1992) 33. [8] VascoMax C-200, C-250, C-300, C-350, Teledyne Vasco, Paramount, CA, 1982. [9] J.W. Dini and H.R. Johnson, Plat. Surf. Finish., 64 (August 1977) 44. [10] G.A. DiBari, Plating, 52 (1965) 1157. Ell] G.A. DiBari, US Patent 3,338,803, August 1967. [12] J.P. Young, V.A. Lamb, G.I. Reid, J.R. Berkeley and W. Ng, Plating, 57, (1970) 921. [13] J.W. Dini and H.R. Johnson, Met. Finish., 72 (August 1974) 44. [14] Materials selector 1991, Mater. Eng., (December 1990) 49. [15] Met. Prog., 106 (1) (1974) 51. [16] Preparation of and plating on stainless steel, ASTM B 254-70 (ASTM, Philadelphia, PA). [17] J.W. Dini, H.R. Johnson and R.S. Jacobson, in R. Sard, H. Leidheiser, Jr., and F. Ogburn (eds.), Properties of Electrodeposits, Their Measurement and Significance, Electrochemical Society, Pennington, NJ, 1975, pp. 307 318. [18] J.W. Dini and H.R. Johnson, Plat. Surf. Finish., 69 (November 1982) 63. [19] J.W. Dini and H.R. Johnson, Met. Finish., 75 (March 1977) 42; 75 (April 1977) 48. [203 J.W. Dini and H.R. Johnson, in K.L. Mittal (ed.), Adhesion Measurement of Thin Films, Thick Films, and Bulk Coatings, ASTM 640 1978, pp. 305-326 (ASTM, Philadelphia, PA).