The solidification behavior of Ti-48Al-8Nb alloy under nonequilibrium solidification conditions was studied by electromagnetic levitation technique.The solidification conditions are different undercooling（△T）under the same cooling condition and different cooling methods at the same undercooling condition,respectively.In different undercooling conditions,when the undercooling is above a critical value（△T＊≈211K）,a remarkable morphological transition from typical hypoperitectic solidification to a sole solidification of the（3 phase resulting in the suppression of the peritectic reaction occurs.For melts with different cooling conditions at the same undercooling（△T≈85 K）,the melt was rapidly cooled by quenching them in cooling media.With cooling rate increasing,a transition from β phase to peritectic α phase solidification mode is revealed for Ti-48Al-8Nb alloy.
The Ti_(2)AlN-reinforced TiAl(WMS)composites with different contents of Ti_(2)AlN were prepared by an in situ method of reactive arc-melting technique.According to the results of X-ray diffraction(XRD)analysis,the Ti_(2)AlNreinforced WMS composites consist ofγ-TiAl,α_(2)-Ti_(3)Al,and Ti_(2)AlN phases.Microstructure analysis results indicate that Ti_(2)AlN reinforcements with rod-like in shape form in the WMS matrix with aα_(2)/γlamellar structure containing some bulk y phases.With volume fraction of Ti_(2)AlN increasing,the grain size of the composites decreases significantly and the elasticity modulus(E)increases.The compressive strength and compressive fracture strain of the composite with 3 vol%Ti_(2)AlN have a maximum value of 1,654 MPa and 22.5%,respectively,which are approximately improved by 45.84%and 29.31%,respectively,compared with that of the unreinforced WMS alloy.
Wan-Liang LiangRui HuYi-Wen LiuTie-Bang ZhangJin-Shan Li
采用数值计算和试验的方法,研究了直径30~50 mm Ti Al合金铸锭凝固组织的截面尺寸效应。结果表明:受径向散热和轴向散热竞争的影响,Ti Al合金铸锭的宏观组织存在竞争生长区、径向生长区和冒口影响区,随铸锭高径比增大,竞争生长区和冒口影响区占比减小,径向生长区占比增大。在径向生长区内,对于同一Ti Al合金铸锭,随散热距离的增加,柱状晶宽度增大,但增大的幅度逐渐减小;对于不同直径的Ti Al合金铸锭,在相同散热距离处,较大直径铸锭的柱状晶宽度更宽,且不同直径铸锭柱状晶宽度的差值随径向散热距离的增加而增大。通过拟合径向温度梯度和轴向温度梯度与铸锭直径和轴向散热距离的关系,建立了柱状晶生长方向与铸锭直径和轴向散热距离的关系。通过拟合温度梯度和凝固速率与铸锭直径和径向散热距离的关系,并耦合柱状晶宽度与温度梯度和凝固速率的关系,建立了柱状晶宽度与铸锭直径和径向散热距离的关系。
The effect of A1 content on the microstructure and solidification characteristics of Ti-A1-Nb-V-Cr alloys in as-cast and isothermally treated states was investigated using X-ray diffraction （XRD）, scanning electron microscopy （SEM） equipped with energy dispersive spectroscope （EDS）, and transmission electron microscopy （TEM）. The typical solidification characteristics are due to the joint influence of both the crystal temperature range and the solidification path. The wide crystallization temperature range contributes to obtaining coarse dendrites in the as-cast Ti47A17Nb2.5V1.0Cr （at%） alloy solidifying through the peritectic reaction. The β-solidifying Ti46A17Nb2.5V1.0Cr （at%） alloy with the narrow crystallization temperature range is attributed to the formation of a homogeneous finegrained microstructure. However, the crystallization temperature range of Ti48A17Nb2.5V1.0Cr （at%） alloy is equivalent to that of Ti46A17Nb2.5V1.0Cr alloy, but it is solidified by peritectic reaction, leading to the formation of finer dendrites.
Yi LiuRui HuHong-Chao KouJun WangTie-Bang ZhangJin-Shan LiJi Zhang
