Synthesis, microstructure, and properties of high purity Mo2TiAlC2 ceramics fabricated by spark plasma sintering

Yunhui Niu,Bo Dai,Salvatore Grasso,Kuibao Zhang,Shuai Fu,Haibin Zhang,Chunfeng Hu

doi:10.1007/s40145-020-0412-7

Abstract

The synthesis, microstructure, and properties of high purity dense bulk Mo2TiAlC2 ceramics were studied. High purity Mo2TiAlC2 powder was synthesized at 1873 K starting from Mo, Ti, Al, and graphite powders with a molar ratio of 2:1:1.25:2. The synthesis mechanism of Mo2TiAlC2 was explored by analyzing the compositions of samples sintered at different temperatures. It was found that the Mo2TiAlC2 phase was formed from the reaction among Mo3Al2C, Mo2C, TiC, and C. Dense Mo2TiAlC2 bulk sample was prepared by spark plasma sintering (SPS) at 1673 K under a pressure of 40 MPa. The relative density of the dense sample was 98.3%. The mean grain size was 3.5 μm in length and 1.5 μm in width. The typical layered structure could be clearly observed. The electrical conductivity of Mo2TiAlC2 ceramic measured at the temperature range of 2–300 K decreased from 0.95 × 106 to 0.77 × 106 Ω–1·m–1. Thermal conductivity measured at the temperature range of 300–1273 K decreased from 8.0 to 6.4 W·(m·K)–1. The thermal expansion coefficient (TEC) of Mo2TiAlC2 measured at the temperature of 350–1100 K was calculated as 9.0 × 10–6 K–1. Additionally, the layered structure and fine grain size benefited for excellent mechanical properties of low intrinsic Vickers hardness of 5.2 GPa, high flexural strength of 407.9 MPa, high fracture toughness of 6.5 MPa·m1/2, and high compressive strength of 1079 MPa. Even at the indentation load of 300 N, the residual flexural strength could hold 84% of the value of undamaged one, indicating remarkable damage tolerance. Furthermore, it was confirmed that Mo2TiAlC2 ceramic had a good oxidation resistance below 1200 K in the air.

Highlights

In order to explore the reaction mechanisms of Mo2TiAlC2 and synthesize pure Mo2TiAlC2 powder, the sintering was processed at different temperatures
Dense bulk Mo2TiAlC2 ceramics were consolidated by spark plasma sintering (SPS), and the physical and mechanical properties, as well as oxidation resistance, were systematically studied
The conclusions are listed as follows: 1) High purity Mo2TiAlC2 powder could be prepared at 1873 K using Mo, Ti, Al, and C element powders with the molar ratio of 2:1:1.25:2 in the flowing argon

Summary

Introduction

J Adv Ceram 2020, 9(6): 759–768 electrical and thermal conductivities, low hardness, normal thermal expansion coefficient (TEC), high damage tolerance, and thermal shock resistance, being the candidates applied in the industrial and aerospace fields [16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31]. By controlling the solid solute elements, new MAX phases-compounds could be synthesized. Fu et al [40] synthesized high purity dense Mo2Ti2AlC3 sample with a relative density of 99.3% by the hot pressing method and systematically characterized its physical and mechanical properties. In order to fabricate the dense Mo2TiAlC2 ceramics with fine grains, spark plasma sintering (SPS) was adopted based on the merits of on-off DC pulse current to generate discharge plasma, releasing point impact pressure and Joule heat, and accelerating electric field diffusion [41,42,43,44]. Under the condition of short annealing time and high pressure, it is convenient to achieve fine grains in the dense bulks, benefiting for the good mechanical properties. Dense Mo2TiAlC2 ceramics were consolidated by SPS and their physical and mechanical properties, as well as oxidation resistance, were studied

Experimental

Results and discussion

Conclusions