超高温稀土硼化物(Y_(1-x)Yb_(x))B_(6)的制备及力学性能研究

Preparation and Mechanical Properties of Ultra-High Temperature Rare Earth Boride(Y_(1-x)Yb_(x))B_(6)

六硼化钇(YB_(6))高温下结构不稳定限制了其在超高温领域的应用,通过引入Yb元素,可形成高温稳定的(Y 1-x Yb x)B_(6)固溶体。本文以(Y_(0.5)Yb_(0.5))_(2)O_(3)和B 4C为原料采用硼/碳热还原法制备了(Y_(0.5)Yb_(0.5))B_(6)粉体,通过无压烧结实现了陶瓷致密化,并结合密度泛函理论计算综合分析了材料的晶体结构、微观形貌和力学性能。结果表明,在1650℃下热处理,B 4C过量6.25%时合成的(Y_(0.5)Yb_(0.5))B_(6)粉体纯度最高。在2000℃下无压烧结获得的(Y_(0.5)Yb_(0.5))B_(6)陶瓷致密度为95.80%,但晶粒尺寸偏大,可达(80.71±35.51)μm。通过两步烧结法所得陶瓷致密度、晶粒尺寸、硬度和断裂韧性分别为95.47%、(14.54±6.31)μm、(14.53±1.37)GPa和(2.81±0.34)MPa·m^(1/2)。陶瓷断口处与典型的高损伤容限陶瓷Ti_(3)SiC_(2)、Hf_(3)AlN的断口形貌十分类似,表明(Y_(0.5)Yb_(0.5))B_(6)具有良好的损伤容忍度,有望提高超高温陶瓷的韧性与延性。

The structural instability of yttrium hexaboride(YB_(6))at high temperature limits its application in the ultra-high temperature field.By introducing Yb element,high-temperature stable(Y 1-x Yb x)B_(6)solid solution can be formed.In this paper,(Y_(0.5)Yb_(0.5))B_(6)powders were prepared via boron/carbon thermal reduction method using(Y_(0.5)Yb_(0.5))2O 3 and B 4C as raw materials,and the ceramics were densified by pressureless sintering.The crystal structure,microstructure and mechanical properties were investigated based on the experimental results and density functional theory calculations.The results show that the(Y_(0.5)Yb_(0.5))B_(6)powders synthesized at 1650℃have the highest purity when B 4C is excess by 6.25%.(Y_(0.5)Yb_(0.5))B_(6)ceramics have a relative density of 95.80%after pressureless sintered at 2000℃,but the grains are coarse with the average size of(80.71±35.51)μm.The relative density,grain size,hardness and fracture toughness of ceramics obtained by two-step sintering are 95.47%,(14.54±6.31)μm,(14.53±1.37)GPa and(2.81±0.34)MPa·m^(1/2),respectively.The fracture morphology of ceramics is very similar to that of typical high damage tolerance ceramics Ti_(3)SiC_(2)and Hf_(3)AlN,which indicates that(Y_(0.5)Yb_(0.5))B_(6)has good damage tolerance and is expected to improve the toughness and ductility of ultra-high temperature ceramics.