LIQUID PHASE DIFFUSION JOINING OF TITANIUM AND TITANIUM ALLOY

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Direct solid phase diffusion joining and liquid phase diffusion joining used titanium-base filler metals were carried out of beta-type titanium alloy whose compositions were of 75%Ti,21%V and 4%Al and their fundamental joinability was discussed. As a result,in the solid phase diffusion joining, an appreciably high bonding pressure was required to obtain a perfect bonded joint. On the other hand, in the ilquid phase diffusion joining with a titanuim-base filler metal of Ti-20Zr-20Cu-20Ni, a fair bonded joint was achieved by a low pressure and a short bonded time. Also an aging heat treatment after bonding was possible to be remarkably raised a tensile strength of the joint.Compared with the liquid phase diffusion joining of a heat resistant superalloy, in the liquid phase diffusion joining with the titanium-base filler metal,the joint of almost identical structure and composition with those of the base metal was obtained by considerably short bonded time. The isothermal solidification p … More rocess was exhibited to be diffusion controlled by depressant such as copper and nickel.Metallugical examination of a commercially pure titanium joint with the titaniumbase filler metal by using transmission electron microscopy revealed as follows.In holding at the joining temperature, diffusion of depressant of zircomnium,copper and nickel into the base metal, was isothermal solidified rapidly a liquid layer within joint area. The joint area was transformed into proeutectoid alpha-phase and eutectoid in cooling, which formed lameller and rod-like microstructure.Furthermore, in the joing of CPTi, an area of needle-like structure corresponded to that contained copper and nickel more than solid solute limit and according to diffusion progress of their elements during joining the width of area of eutectoid transformation increased initially. However,the width decreased with the lapse of holding time and disappered finally. This reason was clarifyed by metallugical examination and the diffusion theory. Less