| In this paper, diffusion bonding of TA17 titanium alloy to 0Cr18Ni9Ti austenitic stainless steel was carried out with several different ways.Titanium alloy and Stainless steel have been treated with surface self- nanocrystallization(SSNC) process before diffusion bonding. Compared with the specimens without SSNC treated before diffusion bonding, the change of the bonding time, bonding temperature and quality of welded joints were analysed.Microstructure observation,micro-hardness testing, SEM observation, EDS determination and XRD analysis were employed to investigate the structure of the joint and phases on the fracture. The relationship of technique parameters, microstructure and joint strength was also studied. The results as follows:By means of surface mechanical attrition treatment(SMAT), a nanostructured surface layer was formed on the cross-sectional surface of an 0Cr18Ni9Ti austenite stainless steel and TA17 titanium alloy.when the peening pressure was 0.6MPa,treatment time was 5min,the distance from peening gun to the surface of the sample was 3~5cm and the ball diameter was 1mm,the grain size of 0Cr18Ni9Ti austenite stainless steel and TA17 titanium alloy surfaces reached 35nm and 30.1nm. After SMAT, 0Cr18Ni9Ti austenite stainless steel had a deformation layer of about 615μm totally, and thereinto the heavily deformed layer was about184.56μm. The a deformation layer and thereinto the heavily deformed layer of TA17 titanium alloy reached 253.52um and121.81um.Diffusion bonding (CTPDB) at constant temperature and constant pressure was applied to produce SSNC-TA17 titanium alloy / SSNC-0Cr18Ni9Ti stainless steel joints, and the joint strength reached 327MPa when it was bonded at 850℃, 8MPa for 1200s. Calculation result showed that the diffusion coefficient of Fe inβ-Ti was higher, and its diffusion activity energy was lower under the condition of SSNC than under no- SSNC situation when the bonding were carried out at the same temperature in CTPDB.Pulse-pressuring diffusion bonding (PPDB) was used to bond TA17 titanium alloy and stainless steel with SSNC. Effect of parameters on the joint strength was investigated, and the optimized parameters for PPDB were gained as follows:when the temperature under 800℃, bonding temperature was 750℃, impact pressure was 80～150MPa, impact pressuring times was 400 cycles, frequency was 0.5Hz, preserved temperature for 0s before impact and 60s after impact.The joint strength reached 262MPa under the optimized parameters. when the bonding temperature is at 850℃, impact pressure was 8～50MPa, impact pressuring times was 40 cycles, frequency was 0.5Hz, preserved temperature for 0s before impact and 0s after impact, and the joint strength reached 364MPa.The reasults show that bonding temperature has greater influence on the joint strength than impact pressuring times and impact pressure.Comparing with CTPDB, the deformation ability of titanium alloy was higher, the diffusion velocity of atoms around the interface was faster, bonding time was shorter and the joint strength was higher under PPDB condition.The microstructure of titanium alloy / stainless steel joint with SSNC was investigated, and it was found thatγ-Fe,σphase,Fe-Ti intermetallic compounds,β-Ti andα-Ti layers were formed during the bonding process. Fracture analysis showed that CTPDB joints ruptured at the interface between intermetallic compounds,σphase,andβ-Ti layers, while PPDB joints ruptured around the interface between intermetallic compounds andβ-Ti layers in the tension test. |
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