干、湿喷丸强化对TC17钛合金喷丸强化层的影响

Influences of Dry and Wet Shot Peening Process on Strengthening Layer of TC17 Titanium Alloy

目的研究干喷丸与湿喷丸强化对TC17钛合金残余应力场的影响。方法采用干、湿喷丸分别对TC17钛合金表面进行喷丸强化处理,利用X射线衍射仪、EBSD以及硬度仪,分析喷丸强度对材料表层残余应力、显微组织以及硬度的影响。结果喷丸强度为0.20 mmN时,干喷丸最大残余应力在距表面30μm处,湿喷丸最大残余应力在表面;喷丸强度为0.30 mmN时,干、湿喷丸引入的残余应力场层深分别为200、90μm,干喷丸引入的残余应力层更深;喷丸强度为0.40 mmN时,干喷丸最大残余应力为-1191.5 MPa,而湿喷丸最大残余应力为-943.9 MPa,干喷丸引入的最大残余应力比湿喷丸的更大;当喷丸强度增加到0.50 mmN时,干、湿喷丸两种强化工艺均出现过喷丸现象,近表层的残余应力发生松弛,同时硬度值降低。通过EBSD研究发现,随着喷丸强度的增加,TC17钛合金表层组织中α相的小角度晶界比例先增加后减少,当喷丸强度为0.50 mmN时,α相内小角度晶界比例减少,大角度晶界比例增加。结论当喷丸强度较小时,干喷丸强化引入的最大残余应力在次表面,而湿喷丸引入的在表面。当喷丸强度较大时,干、湿喷丸强化工艺均出现过喷丸现象,此时大量小角度晶界转变为大角度晶界,钛合金表层硬度场有所减小,残余应力场发生应力松弛。

This paper aims to study the effect of dry shot peening and wet shot peening on the residual stress field of TC17 titanium alloy.The surface of TC17 titanium alloys was successively strengthened by dry and wet shot peening of different strengths.Using X-ray diffractometer,EBSD and hardness tester,the author analyzed the effect of the two processes on the residual stress field,microstructure and hardness field of titanium alloy.When the shot peening strength was 0.20 mmN,the maximum residual stress introduced by dry shot peening in TC17 titanium alloy was 30μm from the surface,while the maximum residual stress introduced by wet shot peening in TC17 titanium alloy was on the surface.When the shot peening strength was 0.30 mmN,the depth of the residual stress field induced by dry and wet shot peening was respectively 200μm and 90μm.The residual stress introduced by dry shot peening was deeper than that of wet shot peening.When the shot peening strength was 0.40 mmN,the maximum residual stress of dry shot peening was-1191.5 MPa,while the maximum residual stress of wet shot peening was-943.9 MPa.The maximum residual stress introduced by dry shot peening was greater than that of wet shot peening.When the shot peening strength was increased to 0.50 mmN,both dry and wet shot peening processes had experienced overshot peening.The residual stress near the surface layer relaxed and the hardness value decreased.Through EBSD research,it was found that as the shot peening strength increased,the low-angle grain boundary ratio ofαphase in the surface layer of TC17 titanium alloy increased first and then decreased.When the shot peening strength was 0.50 mmN,the proportion of low-angle grain boundaries inαphase decreased,and the proportion of high-angle grain boundaries increased.Results indicate that when the shot peening strength is low,the maximum residual stress introduced by dry shot peening is on the subsurface,while that introduced by wet shot peening is on the surface.When the shot peening strength is high,both the dry and wet shot peening processes have experienced overshot peening.At this time,a large number of low-angle boundaries are transformed into high-angle boundaries,the hardness field of the titanium alloy surface layer is reduced,and the residual stress field undergoes stress relaxation.