The Formation Of Defects On Diffusion Bonding Interface Of Ti Alloys Under Elevated Temperature And Their Effects On The Mechanical Properties

The materials for this work were TA12 and TA15 titanium alloy. Firstly the alloys were bonded under different temperatures, pressures and lasting time. And then, optical microscope(OM) and scanning electron microscope(SEM) were employed to observe the distribution of defects on interface. Thirdly, Tensible tests were carried out to evaluate the mechanical properties of joints. According to the results, the best experimental parameters could be obtained. TA12 titanium alloy has good stability under high temprature. However, the fundermental research for it is limited so that TA12 titanium alloy was choosed as the main material to study the factors of interface defects. In order to provide theoretical basis for the engineering application of TA15 titanium alloy, it was also used to study the effects of artifficial defect on the mechanical properties of joints.The results demonstrated that high quality joints of TA12 titanium alloy were obtained under this condition: 940℃, 2h, 5Mpa,and TA15 titanium alloy were under this condition: 940℃, 2h, 5Mpa. Least defects on the interface, highest plasticity and strength of joints could be obtained under this condition.Both the elements of alloy and the roughness have influences on the form of defects on interface. When TA12 was bonded with TA12, there were some small voids with a small size distributed in the bonding interface. However a straight void throughout the interface could be seen when TA12 was bonded with Ti2 Al Nb. Between TA12 and TA15, no voids could be observed and the bonding line disappears. When the roughness of material was under Ra0.8, its effects on the defects and the mechanical property of joinsts were limited. But obvious changes were found when the roughness was more than 0.8: Voids were found on the bonding interface while the strength, plasticity decreased with the roughness increased.The shape and size of artifficial defects keep stable during the process of diffusion bonding. The results showed that the critical point of the size of defects for mechanical property was 0.8mm.When defect was smaller than 0.8mm, the mechanical property decreased just a little. However, the mechnical properied fell sharply when the defect was larger than 0.8mm.