Microhardness and Macrohardness of as-Cast Nb-Ti-Si-B Alloys

摘要:

为了评估Nb-Si基合金是否能作为刀具材料应用，研究了3个Nb-Ti-Si-B合金(1#: Nb-12Ti-16Si-16B，2#: Nb-23.5Ti-16Si-10B，3#: Nb-20Ti-16Si-1.5B)的显微硬度和宏观硬度。这3个合金分别来自Nb-Ti-Si-B四元体系液相面投影图中的NbB、Nb3B2和Nb3Si初生相区。显微硬度采用HX-1000TM型硬度计测试，选用200 g载荷，加载保持时间为15 s。宏观硬度采用HRC洛氏硬度测试。铌基金属间化合物具有较高的显微硬度：1#合金中NbB的硬度为16.58 GPa、2#合金中Nb3B2的硬度为10.08 GPa、3#合金中Nb3Si的硬度为12.12 GPa。强的化学键和元素的置换互溶是铌基金属间化合物高硬度的影响因素。另外，3个合金的宏观硬度HRc分别为77、75和78，3个合金中都具有一定体积分数的高硬度金属间化合物，这是高的宏观硬度的主导因素。Nb-Ti-Si-B合金的宏观硬度值高于工具钢(HRc~65)和高速钢(HSS, HRc~67)。

Abstract:

In order to evaluate the application possibility of the Nb-Si based alloys as cutting tool materials, we investigated the microhardnesses and the macrohardnesses of three alloys (Alloy 1#: Nb-12Ti-16Si-16B, Alloy 2#: Nb-23.5Ti-16Si-10B, Alloy 3#: Nb-20Ti-16Si-1.5B) selected from NbB, Nb3B2 and Nb3Si primary phase regions, respectively, in liquidus projection of the Ni-Ti-Si-B quaternary system. The microhardnesses were measured at a load of 200 g for 15 s using Hx-1000 TM hardness tester. Macrohardness measurement was performed using a Rockwell C scale (HRc). High microhardnesses were obtained for the Nb-based intermetallics: NbB (16.58 GPa in Alloy 1#), Nb3B2 (10.08 GPa in Alloy 2#) and Nb3Si (12.12 GPa in Alloy 3#), which are attributed to strong covalent bonding and appreciable solid solution hardening in these phases. Furthermore, macrohardnesses (HRc) of these three alloys are all above 70, i.e. 77, 75 and 78, respectively, which are primarily provided by certain volume fractions of the hard intermetallic phases in the Nb-Ti-Si-B alloys. The macrohardness (HRc) values of these alloys are higher than those of carbon tool steels (HRc~65) and high speed steel (HSS, HRc~67).