放电等离子烧结制备Nb-Si-Ti-Al-Hf-Cr合金的显微组织及力学性能

以预合金化的粉末尺寸D50为3.3μm的NbSS固溶体相细粉末,粉末尺寸D50分别为22.1μm和23.5μm的Nb5Si3和Cr2Nb化合物粉末为原料,采用放电等离子烧结技术制备NbSS/Nb5Si3两相合金和NbSS/Nb5Si3/Cr2Nb三相合金,研究显微组织形貌、室温和高温力学性能及高温氧化性能。结果表明:两相合金的显微组织由NbSS基体和呈均匀岛状分布的Nb5Si3组成,三相合金中NbSS有相互连接成基体的趋势,而Nb5Si3和Cr2Nb相也以块状散布在NbSS中。NbSS/Nb5Si3两相合金和NbSS/Nb5Si3/Cr2Nb三相合金的室温断裂韧性值KQ分别达到15.1MPa·m1/2和11.3MPa·m1/2,室温下合金中NbSS相以韧窝型断裂为主,对Nb-Si基合金的室温断裂韧性有利,而Nb5Si3和Cr2Nb相为脆性断裂。1250℃时NbSS/Nb5Si3/Cr2Nb合金的压缩强度高于NbSS/Nb5Si3合金,但当温度上升到1350℃时两者强度出现反转。Cr2Nb相对合金高温抗氧化性能有利,1250℃下静态氧化100h时NbSS/Nb5Si3合金的氧化增重为233mg/cm2,大于NbSS/Nb5Si3/Cr2Nb合金的175mg/cm2。

Microstructure and Properties of Nb-Si-Ti-Al-Hf-Cr Alloys Fabricated by Spark Plasma Sintering

Pre-alloyed NbSS solid-solution fine powder with a D50 size of 3.3μm,pre-alloyed Nb5 Si3 and Cr2 Nb compound powders with D50 size respectively of 22.1μm and 23.5μm were used as raw materi-als,and two-phase NbSS/Nb5 Si3 alloy and three-phase NbSS/Nb5 Si3/Cr2 Nb alloy were fabricated by Spark Plasma Sintering (SPS).The microstructure,mechanical properties and oxidation behavior at room and/or high temperatures were investigated.The results show that the microstructure of the NbSS/Nb5 Si3 alloy consists of the NbSS matrix and the uniformly distributed Nb5 Si3 islands.As for the NbSS/Nb5 Si3/Cr2 Nb alloy,the NbSS phase tends to connect to be the matrix,while the Nb5 Si3 and Cr2 Nb blocks scatter in the NbSS phase.Fracture toughness K Q at room temperature of the two-phase and three-phase alloys are 15.0MPa·m1/2 and 11.3 MPa·m1/2 ,respectively.The NbSS phase is found to fail in a dimple mode under bending,which is greatly beneficial to K Q of the bulk Nb-Si based alloys;while the Nb5 Si3 and Cr2 Nb phases fracture in a brittle mode.At 1250℃,the compressive strength of the NbSS/Nb5 Si3/Cr2 Nb alloy is higher than that of the NbSS/Nb5 Si3 alloy,whereas it is contrary at 1350℃.The Cr2 Nb phase plays a positive role in oxidation resistance at high temperature. Air exposed at 1250℃ for 100h,the oxidation mass gain of NbSS/Nb5 Si3 alloy is 233mg/cm2 ,greater than 175mg/cm2 of the NbSS/Nb5 Si3/Cr2 Nb alloy.