Sn對TiAl基合金燒結致密化與力學性能的影響

Sn對TiAl基合金燒結致密化與力學性能的影響EFFECT OF Sn ADDITION ON DENSIFICATION AND MECHANICAL PROPERTIES OF SINTERED HIGH Nb CONTAINING TiAl ALLOYS

以TiAl-8.5Nb預合金粉末為原料，添加1at.%Sn粉為強化燒結劑，采用無壓燒結技術制備了高致密度的高鈮TiAl合金，探究了Sn添加對TiAl基合金的燒結致密化過程、微觀組織、力學性能的影響規(guī)律。研究表明：添加1at.%Sn元素可降低高鈮TiAl合金粉末的燒結致密化溫度，提高燒結坯的致密度及線性收縮率，從而有利于降低合金組織晶粒度、改善合金綜合性能。添加Sn元素后，合金粉末經1500℃/2h燒結，其致密度可達到99.1%，線收縮率達到9.3%；合金顯微組織為均勻細小的α2/γ全片層結構，片層團尺寸為40-60μm；Sn元素主要固溶于γ相中，使其軸比c/a值及晶胞體積增大；所制備合金的洛氏硬度為50.1HRC，抗壓強度為2938MPa，屈服強度為680MPa，壓縮率為29.1%，其性能指標均高于未摻雜Sn元素的高鈮TiAl基合金。

High Nb containing TiAl alloys (TiAl-Nb) are a new generation of materials for high temperature structural applications because of their low density, high strength and corrosion resistance at elevated temperatures. The alloys can be processed by powder metallurgy (PM) which have more advantages including low cost-effectiveness, near net forming for complex parts with fine grain size and uniform microstructure. However, the alloy powders are difficult to achieve full densification due to their lower sintering activity, which impairs the mechanical performance of sintered parts. The present work focuses on the densification performance of TiAl-Nb alloy powders with 1at.%Sn as sintering aids.The effects of Sn addition on the sintering densification process, microstructure and mechanical properties of sintered alloys were investigated. The results show that 1at.%Sn addition can significantly reduce the sintering densification temperature of alloy powders, and increase the relative density and linear shrinkage of sintered parts. This contributes to control microstructure grain size and improve the comprehensive properties. Sintered with 1500℃/2h, 1at.% Sn containing TiAl-Nb based alloys show the best densification performance, with the relative density of 99.1% and linear shrinkage of 9.3%. The alloy samples exhibit fine and uniform full lamellar microstructure, and α2/γ lamellar colonies are sized about 40-60μm. Sn mainly dissolved into γ phase, leading to the enhancement of axial ratio c/a and unit cell volume. The sintered TiAl-Nb-1Sn samples have been found to possess superior room-temperature mechanical properties, with a hardness of 50.1HRC, a compressive strength of 2938MPa, a yield strength of 680MPa, and a compression ratio of 29.1%, which is obviously higher than those of TiAl-Nb alloys.

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