冷却速率对TC21合金相变行为的影响

采用末端淬火法研究了TC21合金自β相区冷却后冷却速率对合金相变和显微组织的影响,对取自末端淬火试样的不同区域试样进行了OM、XRD、TEM及显微硬度分析。结果表明:冷却速率大于122℃/s时,β相转变形成正交马氏体α″,冷速介于122℃/s和3℃/s之间时,发生块状转变,冷速继续降低,相变由扩散控制,形成两种不同形貌的魏氏体α片层:较平滑的α片层和较曲折的α片层;随冷却速率的降低,合金的显微硬度先增大后降低,冷却速率小于8℃/s后,显微硬度迅速降低。

Influence of Cooling Rate on Phase Transformation of TC21 Alloy

The effects of cooling rates from elevated temperature on phase transformations in TC21 alloy were investigated by using end quenching. Samples from different regions (cooling rates) were analyzed by using optical micrograph (0M), Xray diffractometry (XRD), transmission electron microscopy (TEM), and Vickers microhardness. The results show that cooling rates above 122℃/s result in a martensitic transformation, a massive transformation being observed between 122 and 3°C/s, this ransformation being gradually replaced by diffusion controlled Widmanst?tten α formation with decreasing cooling rate. These α layers was of two types, type 1 having a smoother appearance, type 2 having a zig-zagged appearance. With the cooling rates decreasing, the microhardness of TC21 alloy decreased after increased. When the cooling rates was smaller than 8℃/s, the microhardness of TC21 alloy decreased dramatically.