NiTi Shape Memory Alloy Toughening Al₂O₃ Ceramics

Ceramic has high strength, high hardness, wear resistance, corrosion resistance, electrical insulation features, so it is widely used in daily life, industrial production and high-tech fields, but the roadblock to its application is poor fracture toughness. Therefore, how to improve ceramic toughness and preparation has the extremely vital significance.Over the years, the people through various toughening methods to improve ceramic toughness. The common toughening methods have particle dispersion toughening, fiber and whisker toughening, zirconia phase transformation toughening, composite toughening and self-toughening, etc.At present, because NiTi shape memory alloy with rich phase transition phenomenon, so it is widely used in aerospace, architecture, biomedical and daily life, etc. This paper selects alumina ceramics as substrate, NiTi alloy particles as the second phase composite to alumina ceramic substrate. Through the NiTi alloy martensite transformation to improve the characteristics of alumina ceramic toughness.In this paper, the effect of NiTi alloy on alumina ceramic flexural strength and fracture toughness were tested with a CMT5105 Electromechanical universal testing machine;A HD-1875 hardness testing machine was employed to test the hardness of the composite ceramic;this paper researched the phase composition of composite;by scanning electron microscope to observe and analyze the fracture morphology of ceramic materials, and discuss the toughening mechanism.This paper prepared amorphous NiTi alloy powder by mechanical alloying. After the crystallization processing, made the alloy dispersed homogeneously to alumina substrate. Under 1400℃and 1300℃sintering temperature prepared composite ceramic by hot-press sintering process. Meanwhile this paper made equiatomic NiTi alloy composited to alumina substrate, under 1300℃sintering temperature prepared composites. In the meantime, this paper contrasted their mechanical property to the composite ceramics which were composited NiTi alloy by mechanical alloying.The result indicates that mechanical alloying can prepare amorphous NiTi alloy powder and obtain NiTi alloy which crystalline strcture is body centered cubic after the crystallization. This paper made the alloy powder composited to alumina substrate. Under 1400℃and 1300℃sintering temperature prepared composites, their flexural strength and fracture toughness were obviously improved with the increase of the content of NiTi alloy powder. In the same time, this paper made equiatomic NiTi alloy powder composited to alumina substrate, under 1300℃sintering temperature prepared composites, which mechanical properties constantly improved with the increase of the content of alloy powder, but the hardness remained almost unchanged. Compared to the composites whose second phase was NiTi alloy powder which prepared by mechanical alloying, the mechanical properties of the composites whose second phase was equiatomic NiTi alloy powder were better. Because in mixing process we extended the mixing time which could make alloy powder equably dispersed in alumina substrate, and this could improve the composites density, so the composites strength and toughness could be enhanced.The results of the study show that:when external force in composites, NiTi alloy produced stress induced phase transition. The volume dilatancy in phase transition process could consume energy of crack propagation, in the same time, it could restrain the crack propagation and make the crack deflection which improved the composites fracture toughness;Meanwhile NiTi alloy particle bridge league action could inhibit crack continue to expand and improve the composites toughness.