A CO 2 laser has been employed to join binary Ti 50 Ni 50 and Ti 49.5 Ni 50.5 shape-memory alloys (SMAs), with an emphasis on the shape-memory and corrosion characteristics. Experimental results showed that a slightly lowered martensite start (M S ) temperature and no deterioration in shape-memory character of both alloys were found after laser welding. The welded Ti 50 Ni 50 , with an increased amount of B2 phase in the weld metal (WM), had higher strength and considerably lower elongation than the base metal (BM). Potentiodynamic tests revealed the satisfactory performance of laser-welded Ti 50 Ni 50 in 1.5 M H 2 SO 4 and 1.5 M HNO 3 solutions. However, the WM exhibited a significantly higher corrosion rate and a less stable passivity than the BM in artificial saliva. On the other hand, the pseudoelastic behavior of the laser weld was investigated only for the Ti 49.5 Ni 50.5 alloy, to facilitate tension cycling at room temperature. The cyclic deformation of Ti 49.5 Ni 50.5 indicated that the stress required to form stress-induced martensite ( m ) and the permanent residual strain ( p ) were higher after welding at a given number of cycles (N ), which were certainly related to the more inhomogeneous nature of the WM.
Martensitic stainless steel (403SS) is extensively used for intermediate and low-pressure steam turbine blades in fossil-fuel power plants. The purpose of this investigation is to study the repair of shallow cracks on the surface of 403SS steam turbine blades by infrared repair brazing using rapid thermal cycles. A nickel-based braze alloy (NICROBRAZ LM) is used as filler metal. The braze alloy after brazing is primarily comprised of borides and an FeNi 3 matrix with different amounts of alloying elements, especially B and Si. As the brazing temperature increases, more Fe atoms are dissolved into the molten braze. Some boron atoms diffuse into the 403SS substrate primarily via grain boundary diffusion and form B-Cr-Fe intermetallic precipitates along the grain boundaries. The LM filler metal demonstrates better performance than 403SS in both microhardness and wear tests. It is also noted that specimens brazed in a vacuum have less porosity than those brazed in an Ar atmosphere. The shear strength of the joint is around 300 MPa except for specimens brazed in short time periods, e.g., 5 seconds in Ar flow and 30 seconds in vacuum. The fractographs mainly consist of brittle fractures and no ductile dimple fractures observed in the scanning electron microscope (SEM) examination. source, providing a rapid heating rate of up to 3000 ЊC/
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