Erosion Behavior of Gas Tungsten Arc Welded TiNi Intermetallic Overlay

• Main Authors: Jiun-Ming Chen, 陳俊名
• Other Authors: Keh-Chang Chen
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/5y2k6h

碩士 === 逢甲大學 === 材料科學所 === 90 === The pseudoelasticity of TiNi intermetallic alloy provides excellent fatigue resistance and cavitation erosion resistance. A variety of surface engineering processes have been proposed using TiNi coating to reduce damage of erosion. It may be a good idea that using the hardfacing process to yield TiNi intermetallic overlay to protect the commonly used materials with a low cost. Gas tungsten arc welding (GTAW) was chosen to yield an overlay by using Ti50Ni50 intermetallic onto SUS 304 stainless steel and JIS S45C medium carbon steel, and structure of TiNi overlay is manipulated by welding current. Solid/gas impingement and cavitation in different solutions were carried out to explore the erosion behavior of the overlay. Experimental results show that using higher current (130 A) produces a larger heat input and residual stress to make the as-welded TiNi overlay on SUS 304 cracked. Because of this, a proper welding current 85A was determined and microstructure of the weld overlay was characterized. It shows a common as-welded dendrite structure. The X-ray diffraction pattern shows that the as-welded overlay on SUS 304 was approximately TiNi-B2, TiNi-B19’, TiNi3 and Ti3Ni4 phases, while it was TiNi-B2 and TiNi3 phase on S45C. Solid particle impact test was carried out to explore the erosion behavior of the overlay. Substrates and TiNi overlays impacted at 45 m/s shows that all the overlay mass loss were higher than bare substrates at any impact angle indicating a poorer resistance to erosion damage, due to the composition of TiNi overlay was changed lead to lose the behavior of pseudoelasticity, and the dendrite structure. TiNi overlay’s erosion rate was increased with increasing impact angle revealing that the TiNi overlay presents a behavior of brittle material. The XRD diffraction patterns after erosion test suggest a lattice distortion without any phase change by the so called pseudoelasticity. A post heat treatment for the TiNi overlay can reduce internal stress and increase toughness to improve the TiNi overlay erosion resistance. This, however, is helpless to eliminate dendrite structure. Cavitation resistance was evaluated using the ASTM G32-92 standard test in fresh water, 3.5 wt% NaCl water solution and 3.5 wt% HCl water solution. Experimental results show that TiNi overlay in the three solutions significantly increase cavitation resistance. Again, the overlay XRD diffraction patterns after cavitation test suggest a lattice distortion without any phase change. The excellent cavitation resistance due primarily to the higher hardness of the overlay itself. The DC polarization behaviors of TiNi overlay were measured to explore the electrochemical behavior in corrosion environments. It shows that the TiNi overlay in both 3.5 wt% NaCl solution and 3.5 wt% HCl solution exhibit higher corrosion potential and lower corrosion current than the bare substrates. This brings a positive effect to the cavitation resistance.