Investigation On Mechanical And Oxidation Resistance Properties Of Ternary Layered Moalb Alloy

MoAlB is a MAB phase material,which belongs to the cermet type.It has good mechanical properties and high temperature oxidation resistance,so it is expected to be used in the field of high temperature structural materials.Preparation of high-density MoAlB materials with high purity and excellent performance is one of the hot research directions at home and abroad.In this paper,the ternary layered compound MoAlB was prepared by vacuum hot pressing sintering process.By studying the effect of raw material ratio and process parameters on phase composition,the optimal raw material ratio and preparation process parameters were determined.The phase composition,microstructure,mechanical properties and high temperature oxidation resistance of MoAlB materials doped with different content La2O3 were studied.The influence of La2O3 content on the structure and properties of MoAlB alloy was revealed,and discussed the high temperature oxidation resistance mechanism of MoAlB and MoAlB-La2O3 alloy.The research shows that MoAlB alloys prepared by hot pressing of three elemental powders can obtain MoAlB alloys with good performance.When the composition ratio is Mo:Al:B=1:1.1:1,the main phase of the prepared alloy is MoAlB phase with high purity.As the content of La2O3 increases,the grain size of MoAlB alloy gradually refines.The room temperature mechanical property test results show that with the increase of La2O3 content,the density,microhardness,room temperature compressive strength and flexural strength of the alloy are improved,and the fracture toughness is increased by a small amount.When the doping amount of La2O3 is 0.9wt.%,The mechanical properties(compressive strength and flexural strength are 2008MPa and 396MPa respectively)are better than those of the alloys with other doping amounts.Observation of fracture morphology reveals that MoAlB alloy is a typical brittle fracture,showing a mixed fracture morphology of intergranular fracture and transgranular fracture.Among them,the alloy doped with La2O3 is dominated by transgranular fracture,supplemented by intergranular fracture,and there are traces of La2O3 falling off or pulling out.After the MoAlB alloy is oxidized in the air at 1200℃,the oxidized weight gain is 0.74mg/cm2,and the thickness of the oxide layer is about 4 μm.After adding La2O3,the weight gain of the alloy and the thickness of the oxide film increased significantly,indicating that the addition of lanthanum oxide has a significant effect on the high temperature oxidation resistance of MoAlB alloy.Studies have shown that during high-temperature oxidation,the doping of La2O3 accelerates the diffusion of Al to the surface of the alloy,so that the alloy surface layer quickly form an aluminum oxide protective film,which is beneficial to slow down the further oxidation of the alloy matrix.In addition,XRD test results show that the volatilized molybdenum reacts with La2O3 during high temperature oxidation to form a liquid phase of lanthanum molybdate The oxygen atoms have a certain diffusion coefficient in lanthanum molybdate,which can react with the Al element and continue to generate alumina protection membrane.