Journal of Materials Processing Technology最新文献

Laser rescanning is often used as a post-process treatment during Laser Powder Bed Fusion (LPBF) processes to improve product quality. Taking AlSi10Mg material as a case, this study presents a 3D mesoscopic Cellular Automaton (CA) model coupled with Finite Element Analysis (FEA) to simulate grain structure evolution during the Laser Powder Bed Fusion process and its subsequent laser rescanning treatments incorporating non-equilibrium effects under rapid solidification conditions. A key focus of our investigation centers on exploring the potential origins of grain refinement during the laser rescanning process, and the subsequent impact on the resultant grain structure. Our model introduces two key innovations: (i) a diffusion-based grain growth function that tracks composition redistribution during solidification, enhancing the accuracy of grain structure prediction, and (ii) a novel fusion boundary nucleation model that accounts for local composition variations, providing deeper insights into grain refinement mechanisms. By incorporating epitaxial growth, bulk nucleation and fusion boundary nucleation models, we have observed a mixed grain structure in the melt pool, mirroring experimental findings in other studies, delineated into three zones: fine grains at the melt pool boundary (Zone I), long columnar grains (Zone II), and fine equiaxed grains (Zone III). Two factors contributing to grain refinement in our model are presented: (i) Columnar to equiaxed transition (CET) and elevated cooling rate within the rescan melt pool; (ii) Extending volume of fine grains near the rescan melt pool boundary due to fusion boundary nucleation. As a result, laser rescanning treatments, notably, yielded a refined grain structure with approximately 20% reduction in grain dimensions and a pronounced texture under current process parameters. The implications of these findings hold potential for optimized Laser Powder Bed Fusion processes and grain refinement control in future applications.

The interfacial bonding strength of Ti/steel clad plates is a crucial factor that affects their application. However, the effect of the surface state, which is a significant determinant, is often neglected. In this study, various surface treatment processes were employed to create different surface states based on the hot-rolling of double-layer steel billets, and the effects and mechanisms of these surface states on the bonding performance of hot-rolled Ti/steel clad plates were systematically examined. The results showed that the Ti/steel clad plates pretreated with a louver wheel exhibited the highest bonding performance, with the average bonding strength peaking at 328.67 MPa and stabilising at approximately 300 MPa. This strength was approximately 50 % greater than that achieved with wire brush treatment and significantly surpassed the results obtained with sanding belts and diamond grinding discs. The analysis of the surface properties and microstructural characteristics revealed that various surface treatments led to different levels of work hardening and lattice distortion at the surface, and the interface bonding strength depended on the degree of matching between these factors. Proper surface hardening can promote the transformation of lattice distortion energy into a diffusion-driving force of elements on both sides of the interface during rolling, enabling sufficient diffusion of elements on both sides of the interface and obtaining good interface bonding performance. A phenomenological prediction mechanism-based model was established to quantify the relationship between the surface state and the bonding strength. This study elucidats the mechanism by which the surface state of materials influences the interfacial bonding performance of hot-rolled Ti/steel clad plates. These findings have significant implications for enhancing the interfacial properties of these composite plates and for selecting suitable pre-rolling surface treatment processes.

Owing to stray electrochemical discharge effects, it is still a significant challenge to obtain high machining quality and efficiency in conventional electrochemical discharge machining (ECDM) of macro-sized holes (>1 mm) in glass. Thus, in this study, an electrochemical self-discharge machining (EC-SDM) technique using an integrated tool electrode is proposed. In the new design, the tool anode and cathode are configured coaxially in an integral manner. The simulation and high-speed camera observation results indicated that the electrochemical discharges were more concentrated at the tool electrode end when using the EC-SDM. Thus, the stray electrochemical discharge capacity decreased significantly. With the formation of a dense oxidized layer on the anode electrode surface, the EC-SDM technique is frequently interrupted by DC pulse; however, the discharge is continuous under bipolar pulse conditions. Furthermore, the EC-SDM technique can utilize the advantage of the hydrogen-oxygen gas mixture generated at the integrated electrode end for combustion close to the workpiece surface, thus increasing machining efficiency. When compared with the conventional ECDM, the machining efficiency increased by 6.09 times, and the entrance heat affected zone (HAZ) reduced by 54.05 %. A macro-sized hole (entrance diameter of 1303 μm) with depth of 1520 μm, minimal thermal and mechanical damage was successfully obtained in the glass substrate by using the EC-SDM technique. The results illustrate that employing the novel EC-SDM technique is a straightforward way to reduce stray electrochemical discharge and improve the machining performance of macro-sized glass holes. The potential of the EC-SDM technique for MEMS applications was also highlighted.

Reducing grain size is a well-established method for strengthening metals. In this study, a novel severe plastic deformation technique—combined extrusion and torsion (CET) with composite strain—was developed to fabricate bulk ultrafine grained metals. A single pass of CET treatment (with a rotation velocity of 1 r/s and extrusion speed of 3 mm/s) refined coarse-grained copper from 54 μm to 450 nm at room temperature, resulting a significant increase in hardness from 0.55 GPa to 1.3 GPa. The CET technique addresses the limitations of conventional extrusion-processed copper (without torsion), which suffers from gradient microstructure and hardness distribution. It provides enhanced strain accumulation under the same extrusion ratio conditions. The more homogeneous microstructures and properties of CET-processed copper rods are attributed to the reduced strain gradient due to torsion. Additionally, targeted finite element analysis indicated that the CET technology requires 37 % less extrusion load and offers at least 30 % more strain compared to conventional extrusion methods. Compared with other severe plastic deformation methods, such as equal channel angular pressing and high-pressure torsion, which involve simpler deformation processes, the CET technique shows considerable promise for large-scale manufacturing of ultrafine-grained metals.

In the present study, the anisotropic formability and underlying deformation mechanism of near-α TA32 titanium alloy sheet under continuous nonlinear strain paths (CNSPs) at high temperature were investigated in depth. To achieve this goal, a new experimental method combining hot gas bulging with step-combined dies was proposed, and the hot CNSPs of metal sheets can be flexibly and conveniently realized by changing the number and shape of step-combined dies. Based on this method, the anisotropic deformation behavior and forming limits of TA32 sheet under fifteen CNSPs were tested at 800 ℃ with a strain rate of 0.001 s⁻¹. Then, two advanced constitutive models with different scales were embedded into the classical Marciniak-Kuczyński (M-K) theory to predict the forming limits of TA32 sheet under different strain paths: the macro-scale viscoplastic model coupled with Hill48 yield criterion and non-associated flow rule (NAFR) as well as the meso-scale three-dimensional crystal plasticity finite element (CPFE) model coupled with cellular automata (CA). The results demonstrate that the CPFE-CA-MK coupled model exhibits higher accuracy in predicting the forming limits of TA32 sheet under linear and continuous nonlinear strain paths. Especially for the tension-tension strain paths, the CPFE-CA-MK coupled model improves accuracy by at least 3.1 % compared to macro-scale models. Due to the material anisotropy, the initial inclination angle of the groove in the CPFE-CA-MK model is closely related to the strain path and significantly affects the prediction accuracy. Based on the CPFE simulation, the effects of anisotropy and strain path change on the dislocation slip mode of different texture components was analyzed in depth, which provides a theoretical guidance for the optimization of hot forming process of TA32 titanium alloy complex components.

In this paper, porous composites with bi-continuous interpenetrating aluminum foam (AF) and lattice structure were prepared via different sequences. The effect of the preparation sequence on the mechanical properties was analyzed. The results showed that the composites prepared by disordered-ordered and ordered-disordered sequences had higher mechanical properties than the sum of their single components. Porous composite prepared by the disordered-ordered sequence had a discontinuous interface while the one prepared by the ordered-disordered sequence presented a continuous bonding interface and a bubble-free layer. The energy absorption of the porous composite structure prepared by the disordered-ordered sequence was enhanced by the factors of 0.89 and 1.12 over the sum of their single components, while the ordered-disordered was enhanced by the factor of 1.9 and 3.81, which was attributed to the metallurgical bonding, 3D mechanical constraints and the fraction of bubble-free layer that formed between the interfaces. The continuous interface contributed the excellent mechanical properties of the composites due to its higher failure strength before detaching. The presence of the bubble-free layer increased the interfacial contact area, which can effectively absorb energy and exhibit significant deformation resistance. The porous composite exhibited excellent comprehensive performance, which provided a new idea for the structurally and functionally integrated design of porous composites.

In the present work, two new parameters that influence the bond strength and tensile strength of Al/Cu bimetallic sheets are explored using an innovative hybrid manufacturing process. The innovative hybrid manufacturing process includes engineering of four different microstructures, 1. Ultrafine grained (UFG); 2. Bimodal grained (BM); 3. Fine grained (FG) and 4. Coarse grained (CG) in parent Cu and Al via integration of cryogenic based thermo-mechanical treatment followed by an unique tailored criss-cross surface pattern generation and high deformation roll bonding to develop high performance Al/Cu engineered sheets with four microstructural combinations: UFG‐Al + UFG-Cu, UFG‐Al + BM-Cu, UFG‐Al + FG-Cu and CG‐Al + CG-Cu. The criss-cross pattern aids in initiation of crack at the junctions and fissure formations at cross paths during the roll bonding process. This kind of pattern develops mechanical bond in the form of nugget bunches, which result in enhancement of bond strength in all the microstructural combinations of Al/Cu bimetallic sheets. The ascending order of increase in bond strength-tensile strength synergy of all four engineered microstructural combinations is: CG‐Al + CG-Cu, UFG‐Al + FG-Cu, UFG‐Al + BM-Cu and UFG‐Al + UFG-Cu. The UFG‐Al + UFG-Cu combination has achieved an extraordinary bond strength of 18 N/mm, which is almost 1.6 times the bond strength of its conventional coarse grained counterpart CG‐Al + CG-Cu combination (10 N/mm). Similarly, the UFG‐Al + UFG-Cu combination showed excellent tensile strength of 323 MPa which is around 25 % higher than that of CG‐Al + CG-Cu combination (258 MPa). The engineered UFG microstructure in Al and Cu samples promote the dynamic recrystallization and partial diffusion kinetics at the interface region and established the mechanical and metallurgical bonding between Al/Cu bimetallic sheets during roll bonding process. The adopted surface pattern and the engineered microstructure have enhanced the bond strength and tensile strength of Al/Cu bimetallic sheets both at macro and micro levels. The underlying scientific knowhow for obtaining excellent bond strength-mechanical property synergy in the engineered Al/Cu bimetallic sheets are established.