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Modification of the properties of aircraft engine compressor blades by uninterrupted and pulsed-ion beams
ELSEVIER
Surface and Coatings Technology 96 (1997) 39-44
Modification
of the propgties of aircraft engine compressor blades by uninterrupted and pulsed-ion beams
V.A. Shulov a,*, N.A. Nochovnaya
b, G.E. Remnev ‘, A.I. Raybchikov
’
a Moscow Aciatiotl htitute, 4 ?blokokmxsko~~ shosse, 125871 Moscon~, Russia b All-Rmsim Imtitute of Ariatim Mute&Is, 17 R&o Street, 107005 Moscon: Russia ’ Nidfw PhJhs Imtitute, -0 7 Lenin Street, 634050 Tonlsk, Russia
Received21 June 1996;accepted5 March 1997
Abstract
The influenceof uninterrupted and arc-pulsedion implantation, high-powerion beamtreatment and final annealingregimeson the chemical composition and phase-structuralstate of surface layers and on the surface properties of gas turbine engine compressorbladesmanufacturedfrom refractory alloys\vasinvestigated.Long-termfull-scaletestsof the production and irradiated compressorbladeswere carried out under gas turbine engineoperating conditions. After completion of the tests the physicalchemicalstate of the bladeswasstudied.0 1997ElsevierScienceS.A. Keylrortls: Ion beam;Refractory alloys; Serviceproperties
1. Introduction
The development of advanced technological methods for surface processing of gas turbine engine parts manufactured from refractory alloys is one of the important problems in aviation materials science. This is because of the high cost and great demands placed on these parts, which are exposed to simultaneous effects of constant and cyclic loads, gas oxidation and sulfidization at high temperature, and particle and hydro-abrasive erosion. The turbine and compressor blades determine the exact duration of gas turbine engine operation. Ion-beam treatment is the most advanced method for surface processing of machine parts. These include ion implantation by uninterrupted beams (IIUB) [l], arc-pulsed implantation (API) [2] and treatment by high-power pulsed ion beams (HPPIB) [3]. The essence of the IIUP method consists in irradiation of a target surface by an uninterrupted ion beam at low values of ion current -density (j= l-100 ALAcm-‘). The energy of the ions is greater than 20 keV. Beam formation takes place in gas or solid sources (in the solid sources a vapour phase is * Corresponding author. 0257-8972/97/$17.00 0 1997 Elsevier Science S.A. All rights reserved. PZI SO257-8972(97)00120-5
formed by resistive heating of a- solid phase to -J&Z temperature of its intensive sublimation). Implanters of this type have systems for extraction, acceleration, separation and scanning. The API method is based~o~ir&&&G of a target surface by a pulsed ion beam of microsecond duration at hieh values of ion current densitv in a Dulse (uz, to 1 micm-‘). These beams consist mui
10 to lo3 A cm -2). Pulse
duration is usually equal to 1O-l O3ns. The phenomenon of “blasting emission“ is the basis of HPPIB formation. The influence of these beams on materials is similar to that of nanosecond lasers. The prospects for the application of IIUB, API and HPPTB in the aircraft building industry were analyzed
in [4-61 on-the basis of experimental results obtained during research into the surface state of model samples of refractory alloys irradiated by ion beams. In this connection, the aim of the present paper is to investigate the influence of ion-beam treatment on the surface condition of aviation engine compressor blades and on their properties. including a discussion of results obtained from-long-time engine tests.
40
KA. Shulo~~ et 01. J Surface
mnd Coritings
2. Experimental
N
regimes
and the running
Material blades,
of stage
1 2 3 4 5 6 7 8 9 10 11
VT9,3 VT9, 3 VT9, 3 VT9,3 EP866sh7 EP866sh7 EP718, 8 EP718, 9 VT9,3 VT9, 3 VT9,3
12 13 14 15 16 17 18 19
VT9,3 VT9, 3 VT9,3 VT9,3 VT9,3 VT2su,4 VT9,3 VT9, 3
Ion
E (keV)
3 B B N N La N N+La Sm Sm
-Srn
40 40 40 40 40 30 40 40+30 63 63 63
Sm Hf HI Hf Hf La+B C-!-P tip
63 87 87 87 87 66+30 300 300
1 2 3 4
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Alloy
VT9 VT9 VT9 VT9 EP866sh EP866sh EP718ID EP718ID VT9 VT9 VT9 VT9 VT9 VT9 VT9 VT9 VT2SU VT9 v-l-9 YT9* VT25Y* EP866’C EP718*
70* 10 3015 4015 10+3 30+5 2OJ9 1514 2015 2055 lOi3 413 15+5 1415 17i5 12JlOO
20 20 20 20 5x103 20 20 5 x 103+20 2x 103 2 x 103 2x103
-
2x103 2x lo3 2x lo3 2x lo3 2x103 2x10” 6Ok10 16Ok20
x0 man (at%)
h mBX (nm)
3*1 6,1 12i3 4+1 6tl 20+5 10*3 lOJl5 2313 32 &4 39+5 68+5 lOF5 23,4 3015 38&5 25/8
200 + 20 220 * 20 220 &20 150&30 (6+1)x X+_! 140&20 130 J20 4015 4315 43,5 80+10 35,5 30&i 33+4 4025 32/220 -
-
-
VW
lo3
7w
fW4
j (PA cmW2)
-
39-44
time
Table 2 The influence of ion beam treatment regimes on the concentration profile implanted element at a depth of R,: h,,, - thickness of the ion alloyed emission; A 1I2 -half-width of X-ray lines (Ml); * - production blades) N
96 (‘1997)
a carbide-strengthened steel; and EP718ID - a nickeliron alloy [4-61. The uninterrupted rotating blades have been irradiated by the following ions: C, N, B, La, La and B (LaB,), Sm and H’f, employing the ILU-4, DELTA, Raduga [7] and Temp [8] accelerators. The irradiation regimes (Table 1) were chosen according the
The blades of a gas turbine engine compressor (third, seventh, eighth and ninth stages) were manufactured from various refractory alloys: VT9 - an cx+ p-titanium alloy; VT25U - a pseudo cc-titanium alloy; EP866sh Table 1 The irradiation
Technology
201 201 201 201 211 211 311 311 201 201 201 201 201 201 201 201 201 201 201 201 201 211 311
10 10 10
200 200 200
10 10 10 10 10 30 0.2 0.2
200 200 200 200 200 200 0.05 0.05
characteristics layer; H, -
D
n
(ion cmm2)
(pulses)
IO” 2x10” 3x1017 2x10” 2x1o’q 10” 10” 10’9-I 10” 5x10’” 8x10’” 10”
-
5x10” 10’6
5x10’” 8x10’” 10” 4x10” -
Running r, % (h)
time
-
850 600 600 600 600
3 3
(R, - projective running: Xz,, microhardness; R, - roughness;
850 850
- concentration of IEEE - exe-electron
AliZ (grad 20.06)
H, I MW p=os N
~m&O.Ol)
IEEE (pulses-‘)
0.77 0.83 0.84 0.85
400&30 430130 450 * 30 430+30 460 iy 20 36Oi40 450 * 30 480 & 30 440140 460 i40 400140 560 k 40 53oi50 58Oi30 520250 500 + 50 46Oi50 420530 400 &20 38Ok30 400+30 360$30 420 & 20
0.13 0.12 0.15 0.14 0.19 0.21 0.21 0.20 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.14 0.06 0.10 0.16 0.15 0.20 0.21
130 &20 150+40 220 * 40 200 & 30 420220 240 * 50 soi10 800~100 210120 120530 12Oi30 45i!O 70&20 250+50 200 * 40 110&30 1201-20 140t20 250220 6015 45&S 150$_20 210$-30
1.11 0.85 0.83 0.81 0.89 1.00 0.82 0.78 0.87 0.90 0.93 0.95 0,61 0.65 0.79 0.78 1.02 0.71
!‘.A. Shulo~~ et al. J Surface
and Coatiirgs
determination of optimal ion-beam treatment regimes as made by using thermodynamical methods [S] and generalizing from the experimental data published in [P6] for model samples. Surface conditions of the initial and irradiated blades were studied by means of Auger electron spectroscopy (AES), scanning electron microscopy (SEM), X-ray diffraction analysis, optical microscopy and exo-electron emission (EEE). Furthermore, the roughness and microhardness of the blade surfaces have been measured (R,, H,). The total set of these tests was repeated after final annealing (P= 10-r Pa, 7’=450-650°C ~=2 h). Then the blades passed long-term, full-scale tests under gas turbine engine operating conditions (Table 1). After completion of these tests the surface layers of the blades were investigated by the AES, SEM and X-ray analysis methods, and their following properties were determined: fatigue strength (a-r in MPa; loading frequency, f= 1800-3000 Hz; temperature, T=450-6OO’C; in air; tests based on 2 x lo7 cycles), oxidation resistance (ho, thickness of the oxidized layer), erosion resistance (Anr/S,,; quartz sand with d= SO-120 urn; speed of particles, I/= 200 m s-l; sand load, p =20 nigmm-2; angle of impact, ti=90”)‘. The eroded surfaces of the blades and fatigue cracks were studied by the SEM-fracture method [8,9].
Technology
96 (1997)
39-44
depth, nm Fig. 1. Element distributions in the surface layer of blades manufactured from the VT9 aBoy after ion implantation of B (D =2 x 10” ion cmM2) and annealing (5OO’C, 2 h).
/
1
1
3. Results
Some results of these investigations and tests are presented in Tables 2 and 3 and in Figs. l-5. Comparing these data with the results published in [4-61, the following conclusions can be made. (1) The use of low current ion beams (j- 10 uA cm-‘) allows us to alloy surface layers with thickness from 30 nm (heavy ions) to 0.3 urn (light elements); in addition, the processes of phase formation (finely dispersed precipitations of car-
0
depth, nm Fig. 2. Element distributions in the surface layer of blades manufactured from the VT9 alloy after ion implantation of Sm (D = 5 x 10” ion cm-‘) and annealing (500°C 2 h).
Table 3 Sewice properties of the blades after the prolonged engine tests (X, - microhardness; R, - roughness; n-r - fatigue strength; Am/S, - specific mass loss; the regimes of treatment are presented in Tables 1 and 2) N
Material of blade, stage
H, (MPa) p=O.5 N
4
VT9,3 EP866sh, EP866sh, EP718ID, EP718ID, VT9, 3 VT9, 3 VT9, 3 EP866sh, EP718ID,
84Oi 100 650f30 460 & 30 440*30 440$30 420 i 40 860F30 650&70 600F50 620k50
5 6 I 8 18 19 20 21 22
I 7 8 9
7 9
n-r (MPailO) 510 270 320 355 360 580 420 540 270 295
‘The blades irradiated by the B, LaB,, Sm and Hf ions were not tested in a gas turbine engine.
A~rrjS, (mg mm-z&0.005)
0.060_
O-.065 0.025
0.070 0.065 0.090 -4m.
-
ho (w 25)
R,
(urn kO.01)
(a)
Fig. 3. SEM micrographs of the surface of VT25U titanium alloy blades: (a) production blades: (b) the blade after HPPIB treatment (j=60 A cm-‘; n=?O pulses),
bides, borides, oxides and nitrides are formed) and defect formation (an increase of point and linear defects concentrations [9]) take place in the near-surface layer with thickness h- 1 pm during ion implantation and final heat treatment. (2) The most homogeneous state in surface layers is formed in the IIUB process for light ions at high values of current density (j> 1 mA cm-‘) and doses (D> 10” ion cmm2). Moreover, the depth of ion penetration into the matrix reaches -6 pm and an amorphous state is formed in this layer (in this case, the blades were heated to 600-700°C in spite of their being water-cooled). (3) The distinction between IIUB and API consists in the formation of near-surface zones having great concentrations of implanted components (>70 at.%) and impurities (C, 0), and in the increase
(a)
(b) Fig. 4. SEM micrographs of the surface of VT9 alloy blades after prolonged tests in the gas turbine engine: (a) HPPIB treatment (j= 160 A cm-?); (b) HPPIB treatment (j=60 Acm-“).
of modified surface layer thickness (1~- 1-4 pm) if the pulsed regime of implantation is used (API ). (4) HPPIB treatment of the compressor blades in the melting regimes (j< 60 A cm-‘) and the final annealing allow: the roughness to be decrrased. considerably (smoothing of the blade surface occurs up to R, = 0.06 pm. Fig. 3b); micro-defects of the surface to be eradicated, which it is important for parts having sharp edges; the material strength to be increased on account of the formation of finely dispersed carbide precipitates in the thick 0.2 pm layer and at the expense of an increase in the defect composition as a result of shock waves spreading into the matrix (1z- 100 pm); to form a homogeneous stable structure in a surface layer (the average grain size of
1'.A. Slllrlo~et trl. / Swfflce ml
Coariilgs
~tTillZOiUgJ~
96 (1997)
39-44
43
(a) Fig. 6. SEM micrograph of the surface of VT9 alloy blade in the zone ~ofthe entrance edge after prolonged tests in the gas turbine engine.
(b) Fig. 5. SEM micrographs of the fatigue fracture surface of EP718ID alloy blades after prolonged tests in the gas turbine engine: (a) production blade; (b) the blade irradiated by N.
the titanium alloy blades surface layers was equal to 40-60 urn [6]); and a considerable decrease of the interplate distance during annealing to be achieved. The variations of the physical-chemical state of the blade surface layer determine the operation behavior of these blades during their tests in the gas turbine engine. By using the prolonged machine test, it was shown that the following service properties of the blades (seventh, eighth and ninth stages) can be improved by IIUB (La, B) treatment, despite the small thickness of the modified surface layers: ~-r (by lo-40%); h, (more than twice); Anr/S,, (by 40-200%). This effect is attributed to a lack of erosion force on the surface of the compressor last-stage blades during the course of the tests. As a result, the thin surface layers modified by ion beams have been preserved for the duration of the running
time. The changes of these properties, however, were caused by the following reasons: a variation of the fatigue crack formation mechanism from “surface“ (Fig. 5a) to “under surface” (Fig. 5b) or a decrease of the fatigue furrows step during passage of the fatigue crack through a grain; the formation of La,O, and CrN barrier layers, preventing the diffusion of oxygen into the matrix: and the formation of residual compressive stresses in the thin surface layer (h + 1 urn) which results in an increase of the incubation period during erosion fracture. At the same time, the test results for the third-stage compressor blades, for which the erosion force became the main factor in fracture even at first operation, showed that ion implantation cannot ensure a statistically significant improvement of blade properties. Furthermore, even some decrease of the operating characteristics of the third-stage titanium alloy blades treated by uninterrupted ion beams took place (Table 3). The latter caused the fracture of the thin strengthened layer at the beginning of tests (in particular. the erosion load is a great in zones of the blade entrance edges, Fig. 6). As a result, over a long period of operation, the under surface layer has already been exposed to a load where the residual tensile stresses were formed during irradiation [6,10,11]. The data obtained after the tests of titanium blades irradiated by HPPIB allow us to conclude that ion-beam treatment must be carried out at low values of ion current density (j=60 A cm-‘). In this case, the HPPIB treatment results in the following improvements: G- 1 by 30%; Anz/S,, by more than twices; h, by more than nine times. At the same time, irradiation at high values of ion current density leads to a great decrease in the level of service properties. This was caused by micro-heterogeneities having the form of craters (diameter, 5-100 urn; depth, OS-2 urn) during
44
I’.d. Slmlo~ rt nl. / Surfiicrrind Coatings Technolog~~ 96 (1997) 39-44
the HPPIB treatment at high values of ion current density (Fig. 4). The craters formed are surface concentrations of stresses and lead to the formation of microcracks (or even a crack network) during irradiation or operation of the blades. The reasons for and mechanisms of crater formation are presented in [ 12,131.
4. Conclusion
It was shown by using the engine tests and determination of the surface state of irradiated blades that the use of uninterrupted and arc-pulsed implantation allows us to improve the service properties of these parts dramatically if the erosion force is absent during operation. The HPPIB treatment has better prospects for application in the aircraft engine industry compared with ion implantation because the use of high-power ion beams ensures the modification thicker surface layers and the formation of record low values of surface roughness.
References [l] G.K. Hirvonen, Ion Implantation, Metallurgy, Moscow, 1985, p. 391 (in Russian). [Z] A.I. Ryabchikov, R.A. Nasyrov, Phys. Res. B61 (1991) 48-51. [3] K. Yatsui, Laser and Particle Beams 7 (4) (1989) 733-741. [4] G.E. Remnev, V.A. Shulov, Laser and Particle Beams 11 (4) (1993) 707-731. [5] V.A. Shulov, Universities News. Physics 6 (1994) 72-91.(in Russian) [6] V.A. Shulov, N.A. Nochovnaya. G.E. Remnev. et al., in: Proceedings of the 8th World Conf. on Titanium, Birmingham, Vol. 3, 1996 pp. 21x-2135 [7] A.I. Ryabchikov, N.M. Arzubov. Rev. Sci. Instrum. 63 (1) (1992) 2428-2430. [S] V.A. Shulov, A.E. Strygin, Problems of Strength 11 (1990) 40-46.(in Russian) [9] Yu. P. Sharkeev, et al., Surf. Coat. Technol. 83 ( 1996) 15. [lo] V.A. Shulov. A.E. Strygin, A.M. Sulima, Yu. D, Yagodkin, Wear and Friction 11 (1990) 1030-103Uin Russian) [I 11 R. Wei, Surf. Coat. Technol. 83 (1996) 218. 1121 V.A. Shulov, GE. Rcmnev. N.A. Nochovnaya, Surfacetin Russian) 12 (1993) 110-121. [13] V.A. Shulov, G.E. Remnev, N.A. Nochovnaya, Surface 6 (1995) 77-91.(in Russian)
Surface and Coatings Technology 96 (1997) 39-44
Modification
of the propgties of aircraft engine compressor blades by uninterrupted and pulsed-ion beams
V.A. Shulov a,*, N.A. Nochovnaya
b, G.E. Remnev ‘, A.I. Raybchikov
’
a Moscow Aciatiotl htitute, 4 ?blokokmxsko~~ shosse, 125871 Moscon~, Russia b All-Rmsim Imtitute of Ariatim Mute&Is, 17 R&o Street, 107005 Moscon: Russia ’ Nidfw PhJhs Imtitute, -0 7 Lenin Street, 634050 Tonlsk, Russia
Received21 June 1996;accepted5 March 1997
Abstract
The influenceof uninterrupted and arc-pulsedion implantation, high-powerion beamtreatment and final annealingregimeson the chemical composition and phase-structuralstate of surface layers and on the surface properties of gas turbine engine compressorbladesmanufacturedfrom refractory alloys\vasinvestigated.Long-termfull-scaletestsof the production and irradiated compressorbladeswere carried out under gas turbine engineoperating conditions. After completion of the tests the physicalchemicalstate of the bladeswasstudied.0 1997ElsevierScienceS.A. Keylrortls: Ion beam;Refractory alloys; Serviceproperties
1. Introduction
The development of advanced technological methods for surface processing of gas turbine engine parts manufactured from refractory alloys is one of the important problems in aviation materials science. This is because of the high cost and great demands placed on these parts, which are exposed to simultaneous effects of constant and cyclic loads, gas oxidation and sulfidization at high temperature, and particle and hydro-abrasive erosion. The turbine and compressor blades determine the exact duration of gas turbine engine operation. Ion-beam treatment is the most advanced method for surface processing of machine parts. These include ion implantation by uninterrupted beams (IIUB) [l], arc-pulsed implantation (API) [2] and treatment by high-power pulsed ion beams (HPPIB) [3]. The essence of the IIUP method consists in irradiation of a target surface by an uninterrupted ion beam at low values of ion current -density (j= l-100 ALAcm-‘). The energy of the ions is greater than 20 keV. Beam formation takes place in gas or solid sources (in the solid sources a vapour phase is * Corresponding author. 0257-8972/97/$17.00 0 1997 Elsevier Science S.A. All rights reserved. PZI SO257-8972(97)00120-5
formed by resistive heating of a- solid phase to -J&Z temperature of its intensive sublimation). Implanters of this type have systems for extraction, acceleration, separation and scanning. The API method is based~o~ir&&&G of a target surface by a pulsed ion beam of microsecond duration at hieh values of ion current densitv in a Dulse (uz, to 1 micm-‘). These beams consist mui
10 to lo3 A cm -2). Pulse
duration is usually equal to 1O-l O3ns. The phenomenon of “blasting emission“ is the basis of HPPIB formation. The influence of these beams on materials is similar to that of nanosecond lasers. The prospects for the application of IIUB, API and HPPTB in the aircraft building industry were analyzed
in [4-61 on-the basis of experimental results obtained during research into the surface state of model samples of refractory alloys irradiated by ion beams. In this connection, the aim of the present paper is to investigate the influence of ion-beam treatment on the surface condition of aviation engine compressor blades and on their properties. including a discussion of results obtained from-long-time engine tests.
40
KA. Shulo~~ et 01. J Surface
mnd Coritings
2. Experimental
N
regimes
and the running
Material blades,
of stage
1 2 3 4 5 6 7 8 9 10 11
VT9,3 VT9, 3 VT9, 3 VT9,3 EP866sh7 EP866sh7 EP718, 8 EP718, 9 VT9,3 VT9, 3 VT9,3
12 13 14 15 16 17 18 19
VT9,3 VT9, 3 VT9,3 VT9,3 VT9,3 VT2su,4 VT9,3 VT9, 3
Ion
E (keV)
3 B B N N La N N+La Sm Sm
-Srn
40 40 40 40 40 30 40 40+30 63 63 63
Sm Hf HI Hf Hf La+B C-!-P tip
63 87 87 87 87 66+30 300 300
1 2 3 4
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Alloy
VT9 VT9 VT9 VT9 EP866sh EP866sh EP718ID EP718ID VT9 VT9 VT9 VT9 VT9 VT9 VT9 VT9 VT2SU VT9 v-l-9 YT9* VT25Y* EP866’C EP718*
70* 10 3015 4015 10+3 30+5 2OJ9 1514 2015 2055 lOi3 413 15+5 1415 17i5 12JlOO
20 20 20 20 5x103 20 20 5 x 103+20 2x 103 2 x 103 2x103
-
2x103 2x lo3 2x lo3 2x lo3 2x103 2x10” 6Ok10 16Ok20
x0 man (at%)
h mBX (nm)
3*1 6,1 12i3 4+1 6tl 20+5 10*3 lOJl5 2313 32 &4 39+5 68+5 lOF5 23,4 3015 38&5 25/8
200 + 20 220 * 20 220 &20 150&30 (6+1)x X+_! 140&20 130 J20 4015 4315 43,5 80+10 35,5 30&i 33+4 4025 32/220 -
-
-
VW
lo3
7w
fW4
j (PA cmW2)
-
39-44
time
Table 2 The influence of ion beam treatment regimes on the concentration profile implanted element at a depth of R,: h,,, - thickness of the ion alloyed emission; A 1I2 -half-width of X-ray lines (Ml); * - production blades) N
96 (‘1997)
a carbide-strengthened steel; and EP718ID - a nickeliron alloy [4-61. The uninterrupted rotating blades have been irradiated by the following ions: C, N, B, La, La and B (LaB,), Sm and H’f, employing the ILU-4, DELTA, Raduga [7] and Temp [8] accelerators. The irradiation regimes (Table 1) were chosen according the
The blades of a gas turbine engine compressor (third, seventh, eighth and ninth stages) were manufactured from various refractory alloys: VT9 - an cx+ p-titanium alloy; VT25U - a pseudo cc-titanium alloy; EP866sh Table 1 The irradiation
Technology
201 201 201 201 211 211 311 311 201 201 201 201 201 201 201 201 201 201 201 201 201 211 311
10 10 10
200 200 200
10 10 10 10 10 30 0.2 0.2
200 200 200 200 200 200 0.05 0.05
characteristics layer; H, -
D
n
(ion cmm2)
(pulses)
IO” 2x10” 3x1017 2x10” 2x1o’q 10” 10” 10’9-I 10” 5x10’” 8x10’” 10”
-
5x10” 10’6
5x10’” 8x10’” 10” 4x10” -
Running r, % (h)
time
-
850 600 600 600 600
3 3
(R, - projective running: Xz,, microhardness; R, - roughness;
850 850
- concentration of IEEE - exe-electron
AliZ (grad 20.06)
H, I MW p=os N
~m&O.Ol)
IEEE (pulses-‘)
0.77 0.83 0.84 0.85
400&30 430130 450 * 30 430+30 460 iy 20 36Oi40 450 * 30 480 & 30 440140 460 i40 400140 560 k 40 53oi50 58Oi30 520250 500 + 50 46Oi50 420530 400 &20 38Ok30 400+30 360$30 420 & 20
0.13 0.12 0.15 0.14 0.19 0.21 0.21 0.20 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.14 0.06 0.10 0.16 0.15 0.20 0.21
130 &20 150+40 220 * 40 200 & 30 420220 240 * 50 soi10 800~100 210120 120530 12Oi30 45i!O 70&20 250+50 200 * 40 110&30 1201-20 140t20 250220 6015 45&S 150$_20 210$-30
1.11 0.85 0.83 0.81 0.89 1.00 0.82 0.78 0.87 0.90 0.93 0.95 0,61 0.65 0.79 0.78 1.02 0.71
!‘.A. Shulo~~ et al. J Surface
and Coatiirgs
determination of optimal ion-beam treatment regimes as made by using thermodynamical methods [S] and generalizing from the experimental data published in [P6] for model samples. Surface conditions of the initial and irradiated blades were studied by means of Auger electron spectroscopy (AES), scanning electron microscopy (SEM), X-ray diffraction analysis, optical microscopy and exo-electron emission (EEE). Furthermore, the roughness and microhardness of the blade surfaces have been measured (R,, H,). The total set of these tests was repeated after final annealing (P= 10-r Pa, 7’=450-650°C ~=2 h). Then the blades passed long-term, full-scale tests under gas turbine engine operating conditions (Table 1). After completion of these tests the surface layers of the blades were investigated by the AES, SEM and X-ray analysis methods, and their following properties were determined: fatigue strength (a-r in MPa; loading frequency, f= 1800-3000 Hz; temperature, T=450-6OO’C; in air; tests based on 2 x lo7 cycles), oxidation resistance (ho, thickness of the oxidized layer), erosion resistance (Anr/S,,; quartz sand with d= SO-120 urn; speed of particles, I/= 200 m s-l; sand load, p =20 nigmm-2; angle of impact, ti=90”)‘. The eroded surfaces of the blades and fatigue cracks were studied by the SEM-fracture method [8,9].
Technology
96 (1997)
39-44
depth, nm Fig. 1. Element distributions in the surface layer of blades manufactured from the VT9 aBoy after ion implantation of B (D =2 x 10” ion cmM2) and annealing (5OO’C, 2 h).
/
1
1
3. Results
Some results of these investigations and tests are presented in Tables 2 and 3 and in Figs. l-5. Comparing these data with the results published in [4-61, the following conclusions can be made. (1) The use of low current ion beams (j- 10 uA cm-‘) allows us to alloy surface layers with thickness from 30 nm (heavy ions) to 0.3 urn (light elements); in addition, the processes of phase formation (finely dispersed precipitations of car-
0
depth, nm Fig. 2. Element distributions in the surface layer of blades manufactured from the VT9 alloy after ion implantation of Sm (D = 5 x 10” ion cm-‘) and annealing (500°C 2 h).
Table 3 Sewice properties of the blades after the prolonged engine tests (X, - microhardness; R, - roughness; n-r - fatigue strength; Am/S, - specific mass loss; the regimes of treatment are presented in Tables 1 and 2) N
Material of blade, stage
H, (MPa) p=O.5 N
4
VT9,3 EP866sh, EP866sh, EP718ID, EP718ID, VT9, 3 VT9, 3 VT9, 3 EP866sh, EP718ID,
84Oi 100 650f30 460 & 30 440*30 440$30 420 i 40 860F30 650&70 600F50 620k50
5 6 I 8 18 19 20 21 22
I 7 8 9
7 9
n-r (MPailO) 510 270 320 355 360 580 420 540 270 295
‘The blades irradiated by the B, LaB,, Sm and Hf ions were not tested in a gas turbine engine.
A~rrjS, (mg mm-z&0.005)
0.060_
O-.065 0.025
0.070 0.065 0.090 -4m.
-
ho (w 25)
R,
(urn kO.01)
(a)
Fig. 3. SEM micrographs of the surface of VT25U titanium alloy blades: (a) production blades: (b) the blade after HPPIB treatment (j=60 A cm-‘; n=?O pulses),
bides, borides, oxides and nitrides are formed) and defect formation (an increase of point and linear defects concentrations [9]) take place in the near-surface layer with thickness h- 1 pm during ion implantation and final heat treatment. (2) The most homogeneous state in surface layers is formed in the IIUB process for light ions at high values of current density (j> 1 mA cm-‘) and doses (D> 10” ion cmm2). Moreover, the depth of ion penetration into the matrix reaches -6 pm and an amorphous state is formed in this layer (in this case, the blades were heated to 600-700°C in spite of their being water-cooled). (3) The distinction between IIUB and API consists in the formation of near-surface zones having great concentrations of implanted components (>70 at.%) and impurities (C, 0), and in the increase
(a)
(b) Fig. 4. SEM micrographs of the surface of VT9 alloy blades after prolonged tests in the gas turbine engine: (a) HPPIB treatment (j= 160 A cm-?); (b) HPPIB treatment (j=60 Acm-“).
of modified surface layer thickness (1~- 1-4 pm) if the pulsed regime of implantation is used (API ). (4) HPPIB treatment of the compressor blades in the melting regimes (j< 60 A cm-‘) and the final annealing allow: the roughness to be decrrased. considerably (smoothing of the blade surface occurs up to R, = 0.06 pm. Fig. 3b); micro-defects of the surface to be eradicated, which it is important for parts having sharp edges; the material strength to be increased on account of the formation of finely dispersed carbide precipitates in the thick 0.2 pm layer and at the expense of an increase in the defect composition as a result of shock waves spreading into the matrix (1z- 100 pm); to form a homogeneous stable structure in a surface layer (the average grain size of
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96 (1997)
39-44
43
(a) Fig. 6. SEM micrograph of the surface of VT9 alloy blade in the zone ~ofthe entrance edge after prolonged tests in the gas turbine engine.
(b) Fig. 5. SEM micrographs of the fatigue fracture surface of EP718ID alloy blades after prolonged tests in the gas turbine engine: (a) production blade; (b) the blade irradiated by N.
the titanium alloy blades surface layers was equal to 40-60 urn [6]); and a considerable decrease of the interplate distance during annealing to be achieved. The variations of the physical-chemical state of the blade surface layer determine the operation behavior of these blades during their tests in the gas turbine engine. By using the prolonged machine test, it was shown that the following service properties of the blades (seventh, eighth and ninth stages) can be improved by IIUB (La, B) treatment, despite the small thickness of the modified surface layers: ~-r (by lo-40%); h, (more than twice); Anr/S,, (by 40-200%). This effect is attributed to a lack of erosion force on the surface of the compressor last-stage blades during the course of the tests. As a result, the thin surface layers modified by ion beams have been preserved for the duration of the running
time. The changes of these properties, however, were caused by the following reasons: a variation of the fatigue crack formation mechanism from “surface“ (Fig. 5a) to “under surface” (Fig. 5b) or a decrease of the fatigue furrows step during passage of the fatigue crack through a grain; the formation of La,O, and CrN barrier layers, preventing the diffusion of oxygen into the matrix: and the formation of residual compressive stresses in the thin surface layer (h + 1 urn) which results in an increase of the incubation period during erosion fracture. At the same time, the test results for the third-stage compressor blades, for which the erosion force became the main factor in fracture even at first operation, showed that ion implantation cannot ensure a statistically significant improvement of blade properties. Furthermore, even some decrease of the operating characteristics of the third-stage titanium alloy blades treated by uninterrupted ion beams took place (Table 3). The latter caused the fracture of the thin strengthened layer at the beginning of tests (in particular. the erosion load is a great in zones of the blade entrance edges, Fig. 6). As a result, over a long period of operation, the under surface layer has already been exposed to a load where the residual tensile stresses were formed during irradiation [6,10,11]. The data obtained after the tests of titanium blades irradiated by HPPIB allow us to conclude that ion-beam treatment must be carried out at low values of ion current density (j=60 A cm-‘). In this case, the HPPIB treatment results in the following improvements: G- 1 by 30%; Anz/S,, by more than twices; h, by more than nine times. At the same time, irradiation at high values of ion current density leads to a great decrease in the level of service properties. This was caused by micro-heterogeneities having the form of craters (diameter, 5-100 urn; depth, OS-2 urn) during
44
I’.d. Slmlo~ rt nl. / Surfiicrrind Coatings Technolog~~ 96 (1997) 39-44
the HPPIB treatment at high values of ion current density (Fig. 4). The craters formed are surface concentrations of stresses and lead to the formation of microcracks (or even a crack network) during irradiation or operation of the blades. The reasons for and mechanisms of crater formation are presented in [ 12,131.
4. Conclusion
It was shown by using the engine tests and determination of the surface state of irradiated blades that the use of uninterrupted and arc-pulsed implantation allows us to improve the service properties of these parts dramatically if the erosion force is absent during operation. The HPPIB treatment has better prospects for application in the aircraft engine industry compared with ion implantation because the use of high-power ion beams ensures the modification thicker surface layers and the formation of record low values of surface roughness.
References [l] G.K. Hirvonen, Ion Implantation, Metallurgy, Moscow, 1985, p. 391 (in Russian). [Z] A.I. Ryabchikov, R.A. Nasyrov, Phys. Res. B61 (1991) 48-51. [3] K. Yatsui, Laser and Particle Beams 7 (4) (1989) 733-741. [4] G.E. Remnev, V.A. Shulov, Laser and Particle Beams 11 (4) (1993) 707-731. [5] V.A. Shulov, Universities News. Physics 6 (1994) 72-91.(in Russian) [6] V.A. Shulov, N.A. Nochovnaya. G.E. Remnev. et al., in: Proceedings of the 8th World Conf. on Titanium, Birmingham, Vol. 3, 1996 pp. 21x-2135 [7] A.I. Ryabchikov, N.M. Arzubov. Rev. Sci. Instrum. 63 (1) (1992) 2428-2430. [S] V.A. Shulov, A.E. Strygin, Problems of Strength 11 (1990) 40-46.(in Russian) [9] Yu. P. Sharkeev, et al., Surf. Coat. Technol. 83 ( 1996) 15. [lo] V.A. Shulov. A.E. Strygin, A.M. Sulima, Yu. D, Yagodkin, Wear and Friction 11 (1990) 1030-103Uin Russian) [I 11 R. Wei, Surf. Coat. Technol. 83 (1996) 218. 1121 V.A. Shulov, GE. Rcmnev. N.A. Nochovnaya, Surfacetin Russian) 12 (1993) 110-121. [13] V.A. Shulov, G.E. Remnev, N.A. Nochovnaya, Surface 6 (1995) 77-91.(in Russian)