(華南理工大學(xué) 材料科學(xué)與工程學(xué)院，廣州 510640)
摘 要: 采用真空電弧熔煉技術(shù)結(jié)合水冷銅模快速凝固工藝制備出在一定溫度范圍內(nèi)具有負(fù)熱膨脹行為的系列成分富Ti含量Ti100-xNix(x=38~50，摩爾分?jǐn)?shù)，%)熔鑄態(tài)與吸鑄態(tài)合金。結(jié)果表明：合金的負(fù)熱膨脹行為主要源于升溫過(guò)程中B19′→B2逆馬氏體相變所引起的體積變化。富Ti 含量Ti-Ni合金在室溫下的主要物相為B19′-NiTi相和Ti2Ni相，通過(guò)熱膨脹實(shí)驗(yàn)數(shù)據(jù)和混合定則(ROM)計(jì)算所得的B19′相、Ti2Ni相和B2相的熱膨脹系數(shù)值與文獻(xiàn)報(bào)道實(shí)驗(yàn)結(jié)果非常接近。所制備合金的顯微組織具有明顯擇優(yōu)取向生長(zhǎng)特征，導(dǎo)致合金的負(fù)熱膨脹行為呈現(xiàn)顯著的各向異性。當(dāng)合金中Ni含量增加時(shí)，樣品的負(fù)熱膨脹系數(shù)沿最大冷卻速率方向增大，而在垂直于最大冷卻速率方向上先增大后減小。
關(guān)鍵字: 富Ti含量Ti-Ni合金；負(fù)熱膨脹；顯微組織；相變；快速凝固；各向異性
（School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, China）
Abstract:The conventional cast and suction-cast Ti100-xNix (x=38.0~50.0 (mole fraction, %)) alloys with negative thermal expansion (NTE) behavior were fabricated by vacuum arc melting process combining with rapid solidification technique. The results show that the NTE behavior of the alloys originates from the volume change accompanying the B19′→B2 reverse martensitic phase transformation during heating process. B19′-NiTi and Ti2Ni are the two major phases in Ti-rich Ti-Ni alloys at room temperature, and values of the calculated coefficient of thermal expansion (CTE) of B19′, Ti2Ni and B2 phases by using the rule of mixtures (ROM) agree with the experimental data published in literatures. The significant anisotropic NTE response is attributed to the microstructure of the alloys which exhibits typical preferred grain growth characteristics. With increasing the Ni content, the absolute values of CTE along the maximum cooling direction of the alloys increase, while the CTE perpendicular to the maximum cooling direction increases initially and then decreases.
Key words: Ti-rich Ti-Ni alloy; negative thermal expansion; microstructure; phase transformation; rapid solidification; anisotropic property
