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Microstructures and Mechanical Properties of Directionally Solidified Nb-<I>x</I>Mo-22Ti-18Si <I>In-Situ</I> Composites

2000; Japan Institute of Metals and Materials; Volume: 64; Issue: 6 Linguagem: Inglês

10.2320/jinstmet1952.64.6_474

1880-6880

Hisatoshi Hirai, Tatsuo Tabaru, Hidetoshi UENO, A. Kitahara, Shuji Hanada,

Boron and Carbon Nanomaterials Research

In order to examine the possibility of niobium solid solution/niobium silicides in-situ composites as future high temperature structural materials, directionally solidified Nb-xMo-22Ti-18Si(x=0, 10, 20 and 30) alloys were prepared by the floating zone melting technique. A part of each specimen was annealed at 1870 K in a vacuum for 100 h and examined by optical and scanning electron microscopy. Vickers hardness was measured at room temperature. The high temperature compression strength of annealed specimens was measured at 1470 and 1690 K in a vacuum at an initial strain rate of 1×10−4 s−1.By adding molybdenum, the microstructure became finer and the silicide changed from (Nb, Ti)3Si to (Nb, Mo, Ti)5Si3. The Vickers hardness of annealed specimens increased almost linearly with increasing molybdenum content, from 510 to 880. At 1470 K, a specimen with x=0 displayed high yield stress, but it fractured at a small plastic strain. As for specimens with x=10, 20 and 30, yield stress, maximum stress and compressive ductility increased with increasing molybdenum content. At 1690 K, specimens with x=0 and 10 had the higher maximum stress than the others, but they showed a sharp decrease in stress after reaching the maximum stress because of easy cracking. On the other hand, specimens with x=20 and 30 showed lower yield stress and maximum stress than those with x=0 and 10. They showed small stress drop after reaching the maximum stress, however, and almost constant flow stress of 330 MPa(x=20) and 400 MPa(x=30) for large strain range without any apparent cracking.