Key Engineering Materials Vol. 871

Abstract: To improve the mechanical properties of a sintered WHA using high entropy alloy as the matrix (W-HEA), investigations were carried out to apply deformation strengthening method of hot swaging on the W-HEA. The W-HEA samples were swaged around 1300°C with the 10%, 15% and 20% of reduction in area. The results show that the strength and hardness of the W-HEA composite increased with the increasing degree of deformation. And the aspect ratio of tungsten grains increases along the axial direction in the swaged alloys. The hardness of W-HEA with a 20% reduction in area reaches 448 HV, and the dynamic compression yield strength is about 1911 MPa. After hot swaging, the hardness and strength of the W-HEA are greatly improved compared with the sintered W-HEA.

Abstract: Stainless steel is more and more widely used in industry and life. 304 stainless steel has been widely used because of its lower price and better corrosion resistance. In this paper, according to the phenomenon of the crack of the adapter strip made of 304 stainless steel when used on the ship, the reason of the crack is analyzed from the aspects of design, technology and use, and the reasons of the crack are finally determined. In this paper, the mechanism of welding stress and chlorine embrittlement are analyzed and the corresponding improvement strategies are developed.

Abstract: The vehicle axle is the main bearing part of the vehicle transmission, which needs to carry large power and torque. The axle is processed with high-strength steel. In order to verify the material properties of the axle and confirm whether it meets the design requirements, the chemical composition, mechanical properties, microstructure and metal inclusions of the axle are analyzed. The results show that the chemical composition of the material used in the axle meets the standard requirements, the parts with high hardness and tensile strength are tempered martensite, and the metal inclusions are mainly alumina inclusions, silicate inclusions and tin inclusions. Through the analysis of the performance of the axle, it is concluded that the axle material can meet the design requirements.

Abstract: Traditional high-throughput experiments increase the test efficiency by designing component gradient tests and other methods. This article intends to improve the traditional high-throughput experiments and proposes an experimental scheme combining nanoindentation technology and electron probe microanalysis (EPMA). Based on a new Ti-Mo-Al-Zr-Cr-Sn alloy, micro-region composition and corresponding performance at multiple indentations are directly characterized, including a series of different alloy compositions composed of 8 elements such as Mo, Al and the corresponding hardness (H) and elastic modulus (E). Then the principal analysis method in statistics, the theory of molybdenum equivalent and aluminum equivalent are used to process the obtained data, and a series of atlases such as "E-H-component characteristic parameters" and "E-H-alloy equivalents" are constructed, which has achieved high-throughput characterization of the relationship between composition and performance of titanium alloy. Related work can not only quickly determine the alloy composition range corresponding to high E and high H values, but also provide guidance for further optimization of titanium alloy composition design.

Abstract: The quality of heavy ingot normally depends on the processing factor and ingot mould type. Based on the ingot mould type only, the quality and solidification process of a 96-ton ingot moulds with different slenderness-ratios have been studied numerically using the software package ProCAST. The results show that the position of shrinkage porosity moves up and the macroporosity in the ingot center increases prominently as slenderness-ratio increasing, meanwhile, the inclusion-floating time through the middle and bottom part of ingot decreases, and A-segregation alleviates as well. The correlation between the quality and slenderness-ratio of the ingot is not a liner relationship, when the slenderness ratio is 1.4, the ingot has better quality.

Abstract: To study quantitatively the effect of heat treatment on the microstructure, composition and mechanical property in a new single crystal nickel-based superalloy for industrial gas turbine (IGT) applications, the eutectic fraction, carbide fraction, and the fraction, size, shape and distribution of the γ ́ phase was characterized by quantitative metallographic method, the evolution of chemical composition and hardness between core and inter dendrite was tested through EMPA and nanoindentation. The experimental results indicate that: The eutectic fraction decreases from (0.52±0.08) % to (0.03±0.01) %. The carbides fraction decreases from (0.23±0.04) % to (0.12±0.03) %, and Feret ratio decreases from 3.21±2.54 to 2.14±0.98. The γ ́ fraction increases from (55.66±4.18) % to (73.78±3.24) % in core dendritic region, from (64.82±1.44) % to (70.11±3.10) % in inter dendritic region. The γ ́-size is 406±111(nm) in core dendritic region and 918±384(nm) in inter dendritic region before heat treatment, 359±69(nm) in core dendritic region and 361±57(nm) in inter dendritic region after heat treatment. The γ ́-cuboidal degree is 1.08±0.20 in core dendritic region and 1.14±0.23 in inter dendritic region before heat treatment, 1.08±0.19 in core dendritic region and 1.02±0.14 in inter dendritic region after heat treatment. The solidification segregation coefficient of main segregation elements, such as Re, W, Hf, Ta, Al, and Mo, is closer to 1, with an average decrease of 27% after heat treatment. The hardness and modulus increase in core and inter dendritic, and their inhomogeneity is reduced between cores and inter dendritic. The improvement of properties result from the improvement of size uniformity and cuboidal degree of γ ́, and the reduction of carbides and eutectic through element homogeneity during heat treatment. The solidification segregation coefficient of main segregation elements, such as Re, W, Hf, Ta, Al, and Mo, is closer to 1, with an average decrease of 27% after heat treatment. With the addition of refractory elements, some elements partition to the dendrite core, while other elements tend to accumulate in the interdendritic liquid and then solidify as the interdendritic and eutectic regions during solidification. The hardness and modulus increase in core and inter dendritic, and their inhomogeneity is reduced between cores and inter dendritic. The improvement of properties result from the improvement of size uniformity and cuboidal degree of γ ́, and the reduction of carbides and eutectic through element homogeneity during heat treatment.

Abstract: The effect of tempering process on the microstructure and properties of low alloyed cast steel was studied. The results show that tempered at (200~400)°C, the M/A island of the granular bainite decomposes and carbide precipitates. When the tempering temperature rises to (500~600)°C, the M/A island is completely decomposed, and the carbide aggregates and gradually spheroidizes. With the increasing of tempering temperature, the tensile strength increases first and then decreases, elongation and impact energy show a trend of increasing at first, then decreasing and then increasing. The tempering brittleness occurs at 400°C.

Abstract: Based on the Paris model of fatigue crack growth theory, the fatigue crack growth behaviour of Center Crack Tension (CCT) specimens of laser melting deposited 12CrNi2 alloy steel is studied by extended finite element method (XFEM). The crack growth rules and fatigue life are analyzed by experiment and finite element simulation. The experimental results are in good agreement with the finite element results, which verifies the accuracy of XFEM method to simulate the fatigue crack growth behaviour of laser melting deposited 12CrNi2 alloy steel components. Based on this, the effects of initial crack direction and load amplitude on fatigue crack growth behaviour are discussed. The results indicate that even if the initial crack direction is different, the crack will finally propagate in a direction perpendicular to the load. With the increase of the load amplitude, the fatigue life of the specimen with initial crack decreases exponentially.

Abstract: This study aims to investigate the influences of rare earth element cerium (Ce) on microstructure and mechanical properties of low alloy ultra-high strength steel. The strength, plasticity, and impact toughness of steels with 0.0367% Ce and without Ce were tested. The influence mechanism of Ce on the microstructure and mechanical properties were investigated by scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS) and electron back scattered diffraction (EBSD). The results showed that the addition of Ce improved the comprehensive mechanical properties of low alloy ultra-high strength steel. In particular, the plasticity and toughness were improved obviously. The addition of Ce increased the elongation from 9.47% to 10.49%, and the low-temperature impact energy from 50J to 58J. The elongation and impact energy increased by 10.77% and 16%, respectively. And the yield strength of all samples remained above 1400 MPa. The rare earth element Ce did not change the matrix composition phase which were martensite. However, the addition of Ce increased the proportion of high-angle grain boundary from 33.2% to 40.2%. In addition, the Ce make the inclusions denatured and hence spherical inclusion with small size can be obtained. The EDS results showed that rare earth and harmful elements P and O formed inclusions, which as a purifier for the molten steel and hindered the formation of the large-size composite inclusions.