DZ22定向高温合金的初熔及其控制

含Hf合金的Ni₅Hf相含量超过1.0％（体积）时,在加热示差热分析曲线的1135～1160℃温度范围出现Ni₅Hf熔化峰。 Ni₅Hf相的存在诱发了含Hf铸造镍基高温合金的初熔。低碳或无碳DZ22合金形成更多的Ni₅Hf相,促进了合金的初熔。 通过1150℃/8h预处理可消除合金中的Ni₅Hf相,从而可使最终固溶处理温度提高50℃,取得明显的均化效果,进一步提高定向合金1040℃持久性能。

INCIPIENT MELTING AND ITS CONTROL IN A blRECTIONALLY SOLIDIFIED NICKEL-BASE SUPERALLOY DZ22

The peak at 1135-1160℃ on the DTA curve during heating corresponds to the melting range of Ni5Hf phase as its volume fraction is greater than 1 %.The formation of the Ni5Hf phase induced the incipient melting of Hf-bearing cast nickel-base superalloy. A distinct segregation of Ni5Hf phase between the top and the bottom of the directionally solidified ingots was noticed, and consequently their sensitivities to incipient melting are quite different. It was found that more Ni5Hf phases were formed in the low-carbon or carbon-free zone of the alloy DZ22 and promoted incipient melting of the alloy.By means of a pretreatment at 1150℃ for 8h, Ni5Hf phase can be eliminated and therefore the final solution treatment temperature can be raised nearly 50℃ which brings about a homogenezing effect and further increase in the stress-rupture properties of the alloy at 1040℃.