Journal of Materials Engineering and Performance最新文献

Refractory metals have increasingly attracted the attention of researchers due to their excellent high-temperature strength, thermal conductivity, radiation resistance, and biocompatibility for applications in extreme environments such as aerospace and nuclear industries. However, beyond traditional manufacturing processes, the complex post-treatment process, high cost, and difficulty in manufacturing complex geometry components limit its further application in modern industry. Compared to conventional manufacturing processes, selective laser melting (SLM) technology, an emerging technology, can significantly simplify the production process and has the advantage of manufacturing parts with complex geometry. Therefore, there is increasing research on manufacturing refractory metals using SLM technology. This article describes the current research progress of pure refractory metals manufactured by SLM regarding the preparation process, microstructure, metallurgical defects, and mechanical properties of refractory metals (tungsten, molybdenum, niobium, tantalum, etc.). Generally speaking, there are some technical difficulties in the fabrication of refractory alloys by SLM, summarized in this paper. Finally, the article presented the prospect of developing SLM refractory metals.

TiTaZrNb medium entropy coatings and their nitride forms (TiTaZrNb)Nx were synthesized by direct current magnetron sputtering. The study evaluated the bias voltage affects microstructure, chemical and phase composition of the metallic coatings. Also, the effect of nitrogen flow on the microstructural and tribological properties of the corresponding nitrides was studied. A change in the crystalline structure from BCC for TiTaZrNb coatings to FCC for (TiTaZrNb)Nx was observed. It was associated with the incorporation of nitrogen into the matrix and the consequent formation of a solid solution of (TiTaZrNb)Nx. An increase in the hardness and residual stresses of the metallic coating was observed with increasing bias voltage to − 130 V and of the nitride coating with increasing nitrogen flow to 12 sccm, reaching hardness values of 12.8 GPa and 25 GPa, respectively. A slight reduction in the hardness of the deposited nitride coating was observed at the higher nitrogen flow of 15 sccm, probably due to the formation of the TiN and ZrN phases. The higher hardness and lower wear rate of the (TiTaZrNb)Nx nitride coatings compared to the uncoated M2 steel samples demonstrate the protective effect against wear of these coatings.

Variable polarity plasma arc welding (VPPAW) can be used for the excellent welding of 5A06 aluminum alloy, which is promising for aerospace applications due to its excellent welding performance and small welding deformation. In this paper, the corrosion behavior of the welding specimens was studied by a metallographic microscope, scanning electron microscope, energy dispersive spectrometer, x-ray diffractometer, and electrochemical workstation. The VPPA welded joint metallographic specimens were subjected to salt spray corrosion tests for 24, 54, 84, 114 and 144 h. The results showed that the heat-affected zone (HAZ) is more sensitive to corrosion than the weld metal (WM) and the base metal (BM), which resulted from the existence and distribution of β(Al₃Mg₂) and Al₆(FeMn) phases in welded joints. The corrosion resistance of VPPA welded joints is WM > BM > HAZ. However, salt spray corrosion increased the corrosion sensitivity of the WM. With the increase of salt spray corrosion time, the WM corrosion tendency raised, and the corrosion resistance of WM became lower than the BM. The corrosion rate curve showed an increasing trend at first and then decreased with the increase of corrosion time, and the corrosion rate reached the highest at 84 h.

The low fracture toughness of NiAl at room temperature is one of the critical issues limiting its application in aircraft engines. It has been previously shown that a small addition of rhenium and alumina significantly improves the fracture toughness of hot-pressed NiAl. In this work, NiAl with an admixture of rhenium and alumina was produced by laser powder bed fusion additive technology (LPBF). The purpose was to compare the fracture toughness, bending strength, and microhardness of the NiAl-Re-Al₂O₃ material produced by LPBF and hot pressing (HP). Our results show that the LPBF material has lower fracture toughness and bending strength compared to its hot-pressed equivalent. Microcracks generated by thermal stresses during the LPBF process were the primary cause of this behavior. To improve the LPBF material, a post-processing by HP was applied. However, the fracture toughness of the (LPBF + HP) material remained at 50% of the K_IC of the HP material. This study supports hot pressing as a suitable processing method for NiAl with rhenium and alumina additions. However, a hybrid approach combining LPBF and HP proved to be highly effective on the raw NiAl powder, resulting in superior fracture toughness of the final material compared to that consolidated by singular HP.

It was discussed that the research progress and technical achievements had been obtained in the field of residual stress measurement and control of high-grade and large-diameter welded pipe for oil and gas transportation in China. (1) The layout scheme of measuring points and the requirements of spaces between measuring points, hole depth, etc., for residual stress measurement of welded pipe using hole drilling strain-gage method were proposed. On which, the residual stress measurement technology for welded pipe was proposed. (2) The measurement results indicate that the characteristics and distribution of residual stress of SAWH pipes with different grades and sizes were quite different. In general, the residual stress of SAWH pipe was highest, followed by JCOE pipe and UOE pipe. After the ring splitting test, SAWH pipe section usually had relative displacement in circumferential, axial and radial directions, and the degree of deformation varies greatly; But SAWL pipe section usually only occurs circumferential opening, without axial and radial stagger, and the circumferential opening of JCOE pipe was usually larger than that of UOE pipe. (3) Based on the mechanical analysis of the complex deformation of SAWH pipe after the ring splitting test and the superposition principle of elastic mechanics, a prediction model of the residual stress of the high-grade and large-diameter welded pipe suitable for SAWH pipe was established, which overcame the deficiency of the existing prediction models of the residual stress of the welded pipe only considering the circumferential deformation. (4) The key forming parameters affecting the residual stress of SAWH pipe were analyzed and determined as the reduction and forming angle. Combined with the finite element simulation analysis, field adjustment and residual stress analysis, the forming technology and residual stress control technology of low residual stress SAWH pipe were developed.

In order to enhance the hardness and wear resistance of 316L alloy, a strengthening phase was incorporated and laser-directed energy deposition was utilized to create a composite deposition layer consisting of coarse WC/316L, fine WC/316L, and coarse/fine WC/316L. Microstructural observations, phase composition analysis, Vickers hardness testing, interfacial coupling analysis, x-ray diffraction (XRD), and evaluation of friction-wear performance were systematically performed on the deposited samples. These investigations were undertaken to elucidate the impact of incorporating WC particles on both microstructural features and wear characteristics. Results showed that the average grain size of the composite deposition sample with coarse WC/316L decreased by 24% compared to 316L, with a 15.9% increase in hardness and a 97.6% decrease in wear rate. Similarly, the fine WC/316L composite deposition sample saw a 23% reduction in grain size, a 6.4% hardness increase, and a 62.4% decrease in wear rate compared to 316L. The hardness increased by 6.4%. The wear rate decreased by 62.4%. The coarse/fine WC/316L composite deposition samples exhibited a 34% decrease in average grain size, a 35.9% hardness increase, and a 99.1% decrease in wear rate compared to 316L. The addition of WC significantly enhanced the properties of 316L alloy, with coarse/fine WC showing the most significant improvements in microhardness and wear resistance.

MxV Rail has explored new methods of improving the longevity of both rail and thermite welds. As a part of this research, MxV Rail explored ultrasonic impact treatment (UIT) as a method for increasing thermite weld performance and performed a residual stress investigation to estimate the distribution of the compressive and tensile stresses along the weld cross sections. UIT uses a needle to impart very small and rapid localized impacts to plastically deform the material it is applied to. Weld material reshaping and compressive residual stresses all result from UIT, which produce fatigue life improvements that benefit the life of the weld. A residual stress investigation using latest methods was also executed on both new rails and rails with different amounts of wear to analyze the distribution of estimated stresses. Fatigue defects grow quickly under tensile stresses and slowly under compressive stresses. Since UIT introduces compressive stresses on the surfaces of the weld material, an increase in the life of thermite welds can be expected due to retarded crack growth in localized areas of compressive stresses. In order to estimate the change in stress conditions caused by UIT, MxV Rail analyzed residual stresses in three thermite welds: (1) a UIT-treated new weld, (2) a UIT-treated weld removed from track after 150 million gross tons, and (3) an untreated new thermite weld. The residual stress estimations were accomplished by using hole drilling (HD) and contour methods. While the HD method provides estimated strains along two axes (longitudinal and transverse) at very shallow depths in particular locations, the contour method involves wire electric discharge machining and advanced finite element analysis to estimate the overall longitudinal strains (ε_zz) across the entire cross section of the weld or rail. The contour method was also applied to the rails to better understand the influence of residual stresses due to wheel–rail interaction on the head along with rail wear and how the modified residual stress distribution in worn rail compares to the initial residual stress distribution in a new rail that has been rolled but not laid in track.