Preparation And Failure Mechanism Of Ti/Al Laminate Composites

It is of great significance in high-temperature aeroengine applications for Ti/Al laminate composites to be fabricated into Ti-Al3Ti parts by plastic forming and subsequent vacuum hot pressing. Moreover, Ti/Al laminate composites exhibit the integration and advantages of titanium and aluminum and then have lightweight, high wear resistance, high corrosion resistance, high strength and high stiffness, thus utilized in tall buildings and military application. Therefore, the preparation and failure mechanism of Ti/Al laminate composites are significant for their engineering applications.Firstly, Ti/Al laminate composites were prepared by explosive welding and vacuum hot pressing respectively. The results indicated that Ti/Al laminate composites prepared by explosive welding had a good bonding interface whose metallurgical bonding width was more than 20 ?m. However, the vortex zones at the local areas were on stress concentration and easy to become a crack source, which was not conducive to the subsequent plastic forming. The element mutual diffusion layer width of the Ti/Al laminate composites prepared by vacuum hot pressing reached to 5.2 ?m, less than that of explosive welded laminate composites. Nevertheless, a good interfacial bonding still formed at the hot pressed laminate composites. Furthermore, the hot pressed Ti/Al laminate composites had a higher elongation and lower yield-strength radio than the explosive welded Ti/Al laminate composites,indicating a better plastic forming ability. The optimum hot pressing process parameters were: 0.15 mm-thick Ti plates and 0.1 mm-thick A1 plates, 550 ?×3 h, 10-3 Pa vacuum degree and 3 MPa pressure.Secondly, Ti/Al laminate composites were performed in tension, bending and compression tests to investigate their failure mechaism. It was found that stress concentration formed around the local defect areas of the bonding interface and was easy to initiate micro cracks. The initiation of micro cracks was by the nucleation, growth and aggregation of micro holes. After initiation, cracks extended with each other along the interface until the mutual connection, and then the local delamination occurred at the bonding interface. Subsequently, several local delaminations extended with each other until the mutual connection, finally forming the overall delaminations at the bonding interface.Besides, local delaminations broadened sharply along the loading direction and then several triangular delaminations formed at the local bonding interface. Meanwhile, micro cracks continued to extend along the deepened shear bands, which eventually led to the fracture of the specimens.Finally, the fatigue properties of Ti/Al laminate composites were tested to research their fatigue crack initiation, propagation paths, and fatigue crack growth rates. The fatigue results indicated that fatigue cracks initiated at the edges of fatigue specimens and their initiation mechanism was the serious local plastic deformation resulted from the high stress concentration at the edges of the fatigue specimens. Subsequently, a larger triangular tear formed at the fatigue cracking initiations and the fatigue cracks extended in multiple directions to form a large number of micro cracks, but the main developing direction was still perpendicular to the fatigue loading direction. Meanwhile, the interfacial delaminations formed at the first layer of the critical surface, hindering the initiation and propagation of fatigue cracks and releasing fatigue cycle stresses. Besides, the fatigue crack growth was still relatively stable under 0.5?0.2 stress level, indicating a better fatigue property.