时效温度对非平衡凝固K424合金析出相及硬度的影响

采用铜模喷铸与等温时效相结合的方法,研究了快冷K424高温合金的非平衡凝固组织及其沉淀相析出行为。结果表明,铜模喷铸合金组织发生了显著细化,二次枝晶间距相比铸态大幅降低,溶质偏析的减弱有利于抑制粗大碳化物及共晶组织形成。随铜模内径下降,枝晶形貌由无方向性等轴晶逐渐转变为择优生长的定向枝晶。经800~1000℃等温时效30min后,快冷合金的过饱和固溶体组织中开始析出γ′相。随时效温度提高,沉淀相尺寸及体积分数同时增加。900℃×30min时效后可获得大量细小均匀的球形γ′相,快冷合金的显微硬度(HV)高达478,相比原始非平衡态合金提高了13%。

Effects of Annealing Temperature on Precipitation Phase and Hardness of Non-equilibrium Solidified K424 Superalloy

Non-equilibrium solidification and precipitation behavior of rapidly cooled K424 alloy were analyzed by copper mould spray casting combined with isothermal annealing.The results reveal that microstructure is refined greatly in spray-casted alloy,and secondary dendrite spacing is reduced greatly in comparison with that of as-cast one.Moreover,the relief of solute segregation is beneficial to suppress the formation of coarse carbide and eutectic structure.With the decrease of inner diameter,the dendrite morphology in the K424 alloy is changed from random equiaxed grain to preferred growth of directional mode.After isothermal annealing between 800~1000℃for 30 min,γ′phase is precipitated in non-equilibrium solidified alloy,and its size and volumetric fraction are increased with increasing in aging temperature.Because of the formation of considerable uniform and fine sphericalγ′phase,microhardness of 478 HV can be obtained after holding at 900℃for 30 min,which is 13%higher than that of the initial rapid cooled alloy.