Effect of Composite Addition of Ni and Hf Elements on the Micro structure and Mechanical Properties of Precipitation Strengthened Co-Al-W Superalloy
In this paper,the effects of Ni and Hf on the microstructures of a Co-Al-W alloy were investigated,and the yield strength and ultimate strength of the alloys were measured by compression test at 900 ℃.The experimental results proved thatwhen the content of Hf was 0.5％,the alloy exhibited a dual-yand y'phases structure.When the Hf element was 1％,Co23Hf6 phase presented in 10Ni1Hf alloy,Co23Hf6 phase and Co2Hf phase phases formed in 20NilHf,30Ni1Hf and 40Ni1Hf alloys.The yield strength and ultimate strength increased with the incrementof Ni firstly,then decreased,which peaked at 20Ni.As the Hf content increased to 1％,the ultimate and yield strengths of the 10Ni and 20Ni alloys raised,the ultimate and yield strengths of the 40Ni alloy were the smallest,while the yield and ultimate strengths of the 20NilHf alloy were the maximum.The alloying with minor Hf was preferable.It lead to the formation of deleterious Hf-rich phases in the alloys,when the Hf contents was 1％.The addition of Ni within 20％was beneficial to the alloys and the over addition of Ni degrade the strength of the alloys at elevated temperature.
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