Dewei Deng

Electroplating of Ni–ZrO2 nanocomposite coatings on 40CrNiMo7 alloy

Abstract Ni–ZrO2 nanocomposite coatings were obtained by electroplating using Watts nickel baths with different concentrations of ZrO2 particles in suspension. The substrate was horizontally immersed in the bath to enhance the ZrO2 content in the Ni matrix. X-ray diffraction analysis showed that the presence of ZrO2 leaded to the intensity of crystal face (311) sharply increasing, and, simultaneously, the crystal orientation of (220) was greatly decreased. Observation using scanning electron microscopy indicated that the incorporation of ZrO2 nanoparticles also caused changes in the morphology and size of Ni grains. Although agglomeration of ZrO2 nanoparticles occurs in the deposits, the nanocomposites exhibited a great improvement in wear resistance compared to those of unreinforced Ni coating.

Direct Friction Welding of TiAl Alloy to 42CrMo Steel Rods

The effect of post-weld heat treatment (PWHT) on the mechanical properties and microstructure of direct friction-welded joint between TiAl alloy and 42CrMo steel rods was investigated in this paper. It was found that solid joint between TiAl alloy and 42CrMo steel could be obtained without adding interlayer. After PWHT at 580°C for 2 h, the tensile strength of the joint reached 405 MPa, and fracture happened through the TiAl alloy substrate with quasi-cleavage features. The tempered sorbite formed near the interface, improving the joint strength significantly. It was found that TiFe2, TiAl, and small amount of TiC brittle phases formed at the interface, and the interfacial layer was as thin as 2–5 µm. The precipitated phases were 1 µm in average size, and distributed discontinuously at the interface.

Effect of standard heat treatment on microstructure and properties of borided Inconel 718

Boronizing was applied to Inconel 718. In order to obtain the optimal combination of strength and ductility, the borided Inconel 718 was subjected to standard heat treatment. This consists of solution treatment and then a two-step aging treatment. The borided layer is composed of the compound layer and the boron diffusion zone. Because of the superior hardness of borides, the borided Inconel 718 exhibits a significant reduction in its wear rate and relatively low coefficient of friction (COF) compared with the unborided Inconel 718. The standard heat treatment efficiently promotes the diffusion of boron into the interior of the material and the generation of new borides (Fe2B, CrB). The borided layer with standard heat treatment shows much better wear resistance due to the thicker borided layer (313.76 μm).

Effects of substrate bias on structure and mechanical properties of AlCrTiWNbTa coatings

Abstract AlCrTiWNbTa multielements high entropy alloy films have been synthesised by using magnetron co-sputtering of three binary alloy targets. Effects of substrate bias on the microstructure and mechanical properties of the films are studied. The composition and the crystallographic structure of the films are characterised by an electron probe microanalyser (EPMA) and an X-ray diffractometer respectively. The surface micrographs of the films are described by atomic force microscope (AFM). The microhardness and elastic modulus of the films are measured using a nanoindenter. It is found that the deposition rate of the AlTiWTaNbCr films decreases as the increase in the bias voltage. The microstructure of the deposited films is amorphous. The microhardness and elastic modulus of the films keep at about 12·5 and 180 GPa respectively. The surface roughness is in the range of 0·3–0·5 nm.

Growth mechanism of carbon films from organic electrolytes

Carbon films were prepared on both anode and cathode electrode using methanol as carbon source and their growth mechanisms were discussed. In the cathodic reaction, methyls and hydrogen atoms are dominant reactive species. Hydrogen atoms are believed to play a key role in improving growth rate and stabilizing sp3 phase. For the anodic deposition, OH groups can be easily captured on the anode and make oxygen elements inevitable exist in the films. Raman studies indicate that the G peak for carbon films grew on the anode shift to lower wavenumber.

Microstructural Study of 17-4PH Stainless Steel after Plasma-Transferred Arc Welding

The improvement of the surface qualities and surface hardening of precipitation hardened martensitic stainless steel 17-4PH was achieved by the plasma-transferred arc welding (PTAW) process deposited with Co-based alloy. The microstructure of the heat affected zone (HAZ) and base metal were characterized by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that there are obvious microstructural differences between the base metal and HAZ. For example, base material is transformed from lath martensite to austenite due to the heateffect of the welding process. On the other hand, the precipitate in the matrix (bar-like shape Cr7C3 phase with a width of about one hundred nanometres and a length of hundreds of nanometres) grows to a rectangular appearance with a width of about two hundred nanometres and a length of about one micron. Stacking fault could also be observed in the Cr7C3 after PTAW. The above means that welding can obviously improve the surface qualities.

Microstructure and mechanical properties of friction welds between TiAl alloy and 40Cr steel rods

Direct friction welding of TiAl alloy to 40Cr steel rods was conducted, and the microstructure and mechanical properties of the resultant joints in as-welded and post-weld heat treatment (PWHT) states were investigated. The martensitic transformation occurred and brittle TiC phase formed near the interface due to C agglomeration, which degraded the joint strength and increased the microhardness at the interface in as-welded state. Feathery and Widmanstatten structure generated near the interface on TiAl alloy side. After PWHT at 580 °C and 630 °C for 2 h, the sorbite formed and C dispersed at the interface, leading to the increase of the joint strength from 86 MPa in as-welded state to 395 MPa and 330 MPa, respectively. The heat-treated specimen fractured with quasi-cleavage features through the zone 1 mm away from the interface on TiAl alloy side, but the as-welded specimen failed through the interface.

Research of Fatigue Fracture on Fillet Welded Joints Made of FV520B

The fatigue parameters of welded joints made of FV520B were obtained considering the real operating situations. The fatigue fracture types were divided into two groups. The scanning electron microscope (SEM) was applied to carefully study the fatigue fracture surfaces so as to investigate the fatigue failure mechanisms. The microstructures of the base metal and the weld seam were studied by the metallographic microscope (MM), SEM and TEM in support of the dissimilar mechanical property analysis. The present paper concluded that the fatigue microcracks mainly initiated from the surface near the weld toe and inclusions in the weld seam, the heat-affected zone (HAZ) disappeared due to the postweld heat-treatment processes, and that the fatigue resistance of the base metal was better than the weld seam.

Failure Analysis of Axle Sleeve Made from 2Cr13 Steel

The 2Cr13 axle sleeve, used in N52 water pumps, suffered wear after being tested for a relatively short time and fractured when it was beat under the dynamic load. Optical metallographic microscopy, scanning electron microscopy (SEM) and Vickers hardness tester for the fractured 2Cr13 axle sleeve were used to determine the most probable causes of the failure. The results showed that the failure was mainly due to the inappropriate technological parameters of high frequency induction heating and a large amplitude rotor vibration. Meantime, cracks were easily found not only close to the frayed surface but also in the inner part contributed to the inappropriate parameters. Finally, the proper protections were advised to be used for preventing this type of failure for the axle sleeve from happening again in the further.

The Effect of Heat Treatment on Mechanical and Corrosion Performances of Zr-Nb Alloy

The mechanical performance and corrosion resistance of Zr-Nb alloy (Zr705) treated in different ways is tested, and it is found that those properties of Zr-Nb alloy are significantly affected by heat treatment. The most important parameter of the heat treatment is quenching temperature. The Zr-Nb alloy, quenched below the critical quenching temperature Tcq (a temperature or a range of temperature between 850°C-870°C) presents good corrosion resistance performance, however, quenched above the Tcq gets a higher strength and a lower corrosion resistance. Through the study on the basis of the evidences gotten by means of metallographic, SEM, EPMA and TEM, the conclusion can be drawn as that the effect of heat treatment on the performances of Zr-Nb alloy is primarily because of the mechanism of the distribution change of Nb, the quantity of β-Zr, the morphology of grains. Keywords: Zr-Nb alloy, heat treatment, β-Zr, twins