Heat transfer—A review of 2005 literature

In this study cold gas dynamics spraying (CGDS) was successfully used as a joining process to deposit filler metal between two beveled plates. The technique was also employed to build 3-D freeforms. Verification of conceptual experiments was carried out using conventional zinc feedstock powder. SEM and optical microscopy confirmed that dense deposits were created. No significant difference was observed in the mechanical properties between the freeforms and the weldments. Hardness values of 34 ± 2.5 vs. 33 ± 3.2 HV and bending strength of 127 ± 17 vs. 162 ± 30 MPa were observed, respectively. Examination of the fracture surfaces showed that the strength of the interface is higher than the strength of the freeform itself. The results obtained demonstrate that CGDS will be a viable technique for rapid prototyping or joining assembly for thermally sensitive materials.

Cold gas dynamic spraying as a method for freeforming and joining materials

In this study, Zn/15Al, Al and Inconel 625 coatings were applied on low carbon steel substrates by twin wire arc spray process as a corrosion and wear protection barrier against the marine atmosphere. The wear behavior of the coating layer was characterized by a pin-on-disk apparatus at a combination condition of three normal loads and two sliding speeds. The wear tests were conducted in a 3.5 wt.% NaCl solution to evaluate the wear resistance of the coatings in a corrosive environment. The results suggested that the Inconel 625 coating had a better wear resistance in a 3.5 wt.% NaCl solution as compared to the ZnAl and Al specimens. Zn/15Al coatings revealed less wear resistant in a corrosive environment due to the rupture of the oxide film on the coating surface during wear. For the sacrificial protection coatings of Zn/15Al and Al, the characteristics of surface oxide film play a vital role in the wear resistance of the coating materials.

Wear behavior of thermally sprayed Zn/15Al, Al and Inconel 625 coatings on carbon steel

In this work, the microstructure and sliding wear behaviors of stainless steel (AISI 420) coatings prepared by electro-thermal explosion directional spraying (EEDS) and high velocity arc spraying (HVAS) were comparatively investigated. Results show that the EEDS coatings possess more compact microstructure, higher nano-hardness and nano-elastic modulus, finer bond and better wear resistance than the HVAS coatings. The dominant wear mechanism of EEDS coatings is slight furrow and that of HVAS coatings is serious furrow and delamination.

Microstructure and tribological properties of stainless steel coatings sprayed by two methods based on spraying

The 0·8% carbon steel wire was used to deposit coating, and the coated samples were annealed at 550, 650 and 800°C respectively, which were then quenched in water. The microstructure, phase composition and residual stress of the heat treated coatings were studied and compared with that of the coating without any post-treatment. Results show that the heat treatment processes have significant influences on coating oxide, steel alloy grains and residual stresses. The high carbon steel coating expressed tensile stress after spraying, but when the special quenching process was applied, martensite and bainite were formed in the coating, resulting in expansion of material volume, which made the residual stress of the coating change from tension to compression. The correlation between the microstructure and residual stress strongly informed that phase transformation in the coating should be carefully controlled if spray forming thick coating is aimed.

Z.Y. Zhao

Papers

A numerical simulation of temperature field in plasma-arc forming of sheet metal

Arc spray forming