Synthesis and mechanical properties of Nb2AlC and (Ti,Nb)2AlC
Synthesis and mechanical properties of Nb2AlC and (Ti,Nb)2AlC
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DOI：
10.1016/s0925-8388(02)00756-9
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发表时间：
2002-12
影响因子：
6.2
通讯作者：
I. Salama;T. El-Raghy;M. Barsoum
中科院分区：
文献类型：
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作者：
I. Salama;T. El-Raghy;M. Barsoum
本文报道了Nb 2AlC（实际Nb：Al：C比：52.5±0.5，24.0±0.2和23.5± 0.5at.%，（Ti，Nb）2AlC（实际Ti：Nb：Al：C原子比：24.4±0.5、27.3±0.5、24.0±0.3和24.4±0.5原子%，分别）。采用反应热等静压法，在100 MPa、1600°C下对Nb、石墨和Al 4C 3进行反应热等静压8 h，制备了多晶、完全致密、主要为单相的Nb 2AlC（平均晶粒尺寸为14±2 μm）样品。相同的程序导致主要单相样品的（Ti，Nb）2AlC的平均晶粒尺寸为45 μ m。为了获得更细粒度（15±3 μm）的固溶体样品，将粉末混合物在1450 ℃下热压24 h。贫Al Nb 2AlC样品的a和c晶格参数分别为3.107±0.001和13.888±0.001 μ m;固溶体的相应值为3.077±0.001和13.790±0.001 μ m。由于固溶体的硬度（5.8 GPa）介于Nb 2AlC（6.1 GPa）和Ti 2AlC之间，并且在相当的晶粒尺寸下，Nb 2AlC更强，因此我们得出结论，在该系统中没有发生固溶体强化。在这项工作中探索的所有样品都是相当的损伤容限和抗热震性。在1.5 mm厚的四点弯曲棒中进行300 N维氏压痕，根据晶粒尺寸，强度降低25 - 50%。在水中从1200°C淬火使四点弯曲强度降低40%至70%;即，它不是灾难性的。两种组合物都是应变速率敏感的。与Ti_3SiC_2和冰一样，Nb_2AlC试样的压应力也随着应变速率的降低而降低。与此相反，由于不了解的原因，（Ti，Nb）2AlC样品的强度随着应变速率的增加而降低。Nb 2AlC的晶粒生长动力学相当缓慢;即使在1600°C下退火16 h后也没有观察到明显的晶粒生长。
In this paper we report on the fabrication and characterization of Nb2AlC (actual Nb:Al:C ratios: 52.5±0.5, 24.0±0.2 and 23.5±0.5 at.%, respectively) and (Ti,Nb)2AlC (actual Ti:Nb:Al:C atomic ratios: 24.4±0.5, 27.3±0.5, 24.0±0.3 and 24.4±0.5 at.%, respectively). Polycrystalline, fully dense, predominantly single-phase samples of Nb2AlC, (average grain size ≈14±2 μm) were fabricated by reactive hot isostatic pressing of Nb, graphite, and Al4C3at 1600°C for 8 h and 100 MPa. The identical procedure resulted in predominantly single-phase samples—with an average grain size of 45 μm—of (Ti,Nb)2AlC. To obtain finer-grained (≈15±3 μm) samples of the solid solution the powder mixtures were hot pressed at 1450°C for 24 h. The a and c lattice parameters of Al-poor Nb2AlC samples are, respectively, 3.107±0.001 and 13.888±0.001 Å; the corresponding values for the solid solution are 3.077±0.001 and 13.790±0.001 Å. Since the hardness of the solid solution (5.8 GPa) is in between those of Nb2AlC (6.1 GPa) and Ti2AlC, and, at comparable grain sizes, Nb2AlC is stronger, we conclude that no solid solution strengthening occurs in this system. All samples explored in this work are quite damage tolerant and thermal shock resistant. A 300 N Vickers indentation in a 1.5 mm thick, four-point bend bar decreases the strengths by anywhere from 25 to 50% depending on grain size. Quenching in water from 1200°C reduces the four-point flexural strength by 40 to 70%; i.e., it is not catastrophic. Both compositions are strain rate sensitive. Like Ti3SiC2and ice, and for the same reasons, the compressive stress of the Nb2AlC sample decrease with decreasing strain rate. In contradistinction, and for reasons that are not understood, the strengths of the (Ti,Nb)2AlC samples decrease with increasing strain rates. The grain growth kinetics of Nb2AlC are quite sluggish; no appreciable grain growth was observed even after annealing at 1600°C for 16 h.