精铸K417G合金晶界损伤对其持久性能的影响

Effects of Grain Boundary Damage in Microstructure of Investment Casting K417GAlloy Parts on Stress Rupture Properties

熔模铸造K417G合金低压涡轮工作叶片通常需要进行表面细晶处理,在晶粒度检查过程中容易产生过腐蚀现象。通过试验考察了FeCl3腐蚀剂、CuSO_4腐蚀剂对K417G合金表面及性能的影响。结果发现,当采用CuSO_4腐蚀剂进行不同时间的腐蚀后,合金晶界处的碳化物会脱落而形成晶界损伤。合金在950℃、235 MPa条件下的持久寿命表明,当腐蚀5min时,对合金的持久性能不会产生太大的影响,但是当腐蚀时间延长至20min,合金的持久寿命会大幅度降低。当采用FeCl_3腐蚀剂进行不同时间的腐蚀后,合金晶界处的碳化物不会脱落。合金在950℃、235 MPa条件下的持久寿命表明,当腐蚀5min和20min时,合金的持久性能变化不大,但是当腐蚀时间延长至40min后,合金的持久寿命大幅度降低。这主要是FeCl3腐蚀剂对合金的晶界并没有产生损伤,但是随着腐蚀时间延长,合金枝晶间的疏松有扩大趋势,这导致了持久寿命的降低。因此,采用FeCl_3腐蚀剂用于叶片晶粒度检查较为适宜。

It is necessary to perform surface fine grain treatment on investment casting K417 Galloy low pressure turbine blade,however,excessive corrosion can be easily observed in the alloy during grain degree inspection.Effects of FeCl3,CuSO_4 corrosion agent on surface and properties of the K417 Galloy blade were analyzed.The results reveal that with CuSO_4 containing corrosion agent,carbide at grain boundary of the alloy can be flaked to lead to damage the grain boundary.Stress rupture testing at 950℃ and 235 MPa reveals that effects of corrosion on stress rupture of the alloy can be ignored for 5min,while it is deteriorated sharply for 20 min.With FeCl_3 containing corrosion agent,the flake of carbide at grain boundary of the alloy blade is absent.The stress rupture testing at 950 ℃ and 235 MPa reveals that effects of corrosion on stress rupture of the alloy blade can be ignored for 5min and 20 min,while it is decreased greatly for 40 min,which is attributed to the increase of shrinkage porosity in dendrite of the alloy with increasing in corrosion time.The FeCl_3 containing corrosion agent was adopted to inspect the grain degree of the turbine blade.