Materials Science Forum Vol. 1033

Abstract: It is important to reveal the mechanism of crack growth from non-metallic inclusions because it commonly causes the origin of flaking fracture. In order to observe the cracks initiated from non-metallic inclusions under contact pressure, we performed one-point rolling contact fatigue tests using furnace-induction heated SUJ2 steel. We measured the hardness distribution of the furnace-induction heated (FIH) specimen and observed cracks with the inclusions at cross-sections.

Abstract: The engineering field's main issues are often identified to be estimating the deformation and the strain measurements of the working material. Gauging displacements until the fracture more accurately is crucial in experimental procedures for assessing the chosen material properties. This research paper investigates the commercial magnesium alloy (AZ31B) material using digital images, often called Digital Image Correlation (DIC), which provides complete displacement and strain data information at each timestep rather than utilizing an extensometer. This method provides images taken during the deformation, and subsequently, the material properties computed using correlation software for tested samples. The plastic anisotropy coefficients are computed for test samples that cut down at angles of 0, 45, and 90 to the rolling direction. Also, the tensile test finite element model until the necking region was used to verify the fitted models such as Hollomon power-law and Ramberg–Osgood relationships to define the non-linear relationship between stress and strain. Hence, real models and numerical simulations of incremental forming are created to depict this research work's usefulness to the forming applications.

Abstract: According to the profile processing, two forming processes are proposed, i.e., multi-point stamping forming and multi-point stretch forming. Through the finite element simulation, two forming processes are simulated and compared. The analysis results show that the longitudinal springback and transverse forming error of parts by multi-point stretch forming are smaller than those by multi-point stamping forming, so the multi-point stretch forming process is suitable for processing this kind of aluminum alloy profile.

Abstract: To obtain an A356 aluminum alloy casting with a uniform structure and no internal shrinkage defects, ProCAST software is used to set different filling and solidification process parameters for an A356 aluminum alloy casting with large wall thickness differences, And multiple simulations are conducted to obtain optimized casting process; then, based on the process, the microstructure of the thickest and thinnest part of the casting are simulated. The size, morphology, and distribution of the simulated microstructure of the thinnest part and the thickest part of the casting are very similar. The simulated microstructure is similar to that of the actual casting. This shows that castings with uniform structure and no internal shrinkage defects can be obtained through the optimized casting process .

Abstract: One of the main reasons for the scrap of cast thin-wall frame aluminum alloy castings is deformation and cracking. It is an effective method for solving the problem by predicting the distribution of casting stress, clarifying the size of the deformation and the location of the crack, and taking necessary measures in the process. This paper uses the ProCAST software to simulate the thermal stress coupling of A356 thin-walled frame castings, analyzes the influence of pouring temperature, pouring speed and mold temperature on the stress field distribution of castings, predicts the hot cracking trend and deformation, and optimizes Casting process..

Abstract: Multicomponent dendrite growth is theoretically predicted to optimize solidification cracking susceptibility during ternary Ni-Cr-Al nickel-based single-crystal superalloy weld pool solidification. The distribution of dendrite trunk spacing along the weld pool solidification interface is clearly symmetrical about the weld pool centerline in beneficial (001)/[100] welding configuration. The distribution of dendrite trunk spacing along the weld pool solidification interface is crystallography-dependent asymmetrical from bottom to top surface of the weld pool in detrimental (001)/[110] welding configuration. The smaller heat input is used, the finer dendrite trunk spacing is kinetically promoted by less solute enrichment and narrower constitutional undercooling ahead of solid/liquid interface with mitigation of metallurgical contributing factors for solidification cracking and vice versa. Vulnerable [100] dendrite growth region is predominantly suppressed and epitaxial [001] dendrite growth region is favored to spontaneously facilitate single-crystal columnar dendrite growth and reduce microstructure anomalies with further reduction of heat input. Optimum low heat input (both lower laser power and higher welding speed) with (001)/[100] welding configuration is the most favorable one to avoid nucleation and growth of stray grain formation, minimize both dendrite trunk spacing and solidification cracking susceptibility potential, improve resistance to solidification cracking, and ameliorate weldability and weld integrity through microstructure modification instead of inappropriate high heat input (both higher laser power and slower welding speed) with (001)/[110] welding configuration. The dendrite trunk spacing in the [100] dendrite growth region on the right side of the weld pool is considerably coarser and grows faster than that within the [010] dendrite growth region of the left side in the (001)/[110] welding configuration to deteriorate weldability, although the welding conditions are the same on the either side. Furthermore, the alternative mechanism of crystallography-dependent solidification cracking as consequence of asymmetrical microstructure development and diffusion-controlled dendrite growth of γ phase is therefore proposed. The theoretical predictions are comparable with experiment results. The reliable model is also useful for welding conditions optimization for crack-free laser processing.

Abstract: The solidification temperature range was numerically analyzed to optimize nonequilibrium solidification behavior during ternary Ni-Cr-Al nickel-based single-crystal superalloy weld pool solidification with variation of laser welding conditions (either heat input or welding configuration). The distribution of solidification temperature range along the fusion boundary is beneficially symmetrical about the weld pool centerline in the (001)/[100] welding configuration. The distribution of solidification temperature range along the fusion boundary is detrimentally asymmetrical about the weld pool centerline in the (001)/[110] welding configuration. The stray grain formation and solidification cracking are preferentially confined to [100] dendrite growth region. [001] epitaxial growth region with columnar dendrite morphology is favored at the expense of undesirable [100] growth region with equiaxed dendrite morphology to facilitate essential single-crystal solidification with considerable reduction of heat input. The smaller heat input is used, the narrower solidification temperature range is thermodynamically promoted to reduce nucleation and growth of stray grain formation with decrease of constitutional undercooling ahead of dendrite tip and mitigate thermo-metallurgical factors for morphology instability and microstructure anomalies. Potential low heat input(both decreasing laser power and increasing welding speed) with (001)/[100] welding configuration decreases solidification temperature range to significantly minimize columnar/equiaxed transition (CET) and stray grain formation, and improve resistance to solidification cracking through microstructure control. On both sides of weld pool are imposed by the same heat input, while the solidification temperature range along the fusion boundary inside of [100] dendrite growth region on the right part of the weld pool is spontaneously wider than that of [010] dendrite growth region on the left part to increase solidification cracking susceptibility in the (001)/[110] welding configuration. Furthermore, another mechanism of solidification cracking as consequence of severe solidification behavior and anomalous microstructure with asymmetrical crystallographic orientation is therefore proposed. The theoretical predictions are well verified by experiment results. The useful and satisfactory numerical modeling is also available for other single-crystal superalloys during successful laser repair process without stray grain formation.

Abstract: Single point incremental forming (SPIF) is a choice of interest in many manufacturing industries due to its wide range of applications. Materials such as copper, aluminum, steel, and many others formed various complex shapes through this process. However, the forming process could sometimes result in process defects, which could strongly influence the formed parts' geometric accuracy. The twist defect is one of them, which incrementally twists the forming sheet with a small angle at each forming step. In this paper, twist phenomena in the SPIF process have been investigated both numerically and experimentally. In the experiment, Aluminum Alloy (AA5052) was used to form a truncated pyramid shape, and a room temperature tensile test has been conducted to achieve the material's tensile properties. Then, the material property used in the simulation study of the SPIF using LS-DYNA software, where twist defect, stresses, strain, and thickness distribution are studied. The results from simulation and experiment show significant similarity against the expected results and this conveys that the proposed FE model of the SPIF process can be used to investigate the presence of twist, distributions of stress and strain, and thinning locations in the formed part.

Abstract: The microstructure of coatings with different graphene content and the hardness of cladding layer under different distance between coil and samples were investigated. The results showed that with the increase of graphene, the mean particle size of the powder did not get significantly coarser. The defects and oxides were appeared in the cladding layer and graphene diffused into the substrate. Distance between induction coil and sample has great impact on the hardness of coating, the higher hardness was measured in the distance between 6-8cm. The thermodynamic analysis of coating nucleation was carried out.