TC21合金α+β→β相变时膨胀与合金元素 配分行为

Expansion and Partitioning Behavior of Alloy Elements In α+β→β Phase Transformation of TC21 Alloy

摘要:

采用膨胀法、OM、SEM和TEM研究了TC21钛合金在连续加热过程中α+β→β时线膨胀效应和合金元素的配分行为。结果表明： TC21合金在连续加热过程中α+β→β时长度的变化，一方面来源于密排六方α相向体心立方的β相的转变影响，另一方面合金α相不断溶解过程中伴随着α相稳定元素和β稳定元素在两相中的配分，也会导致试样的轴向长度变化。同时发现在α+β→β过程中，α相中Al元素随着α相不断溶解浓度逐渐下降，而在β相中浓度逐渐升高，由于合金元素Al含量增加对α相体积影响不大，但使β相的体积缩小，这是TC21合金长度收缩的主要原因。然而合金元素Mo、Cr、Nb在α→α+β转变过程中又向α相中扩散，在相互扩散过程中还在α/β界面上出现成分不平衡的现象。

Abstract:

The expansion behavior and partitioning behavior of alloying elements in α+β→β phase transformation of TC21 titanium alloy during continuous heating were carried out by combining dilatometric method, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the change in the length of the TC21 alloy during the continuous heating process results from the transformation of α phase with hexagonal close-packed to β phase with body-centered cubic and macro volume variation which originates from redistribution of α-stabilizers and β-stabilizers in the alloy during the continuous dissolution of α phase when the temperature is over β transformation temperature. It is found that the content of Al element increases in the α phase with the dissolution of α phase, but it decreases in the β phase. Additionally, the increasing content of Al element leads to decrease in volume of β phase, which is also main reason for shrinking of the alloy during α+β→β phase transformation. However, Mo, Cr and Nb element diffuse to the α phase during α→α+β phase transformation, so that the composition imbalance was found at the α/β interface.