Experimental Study on Tensile Properties of a Novel Porous Metal Fiber/Powder Sintered Composite Sheet.
ABSTRACT: A novel porous metal fiber/powder sintered composite sheet (PMFPSCS) is developed by sintering a mixture of a porous metal fiber sintered sheet (PMFSS) and copper powders with particles of a spherical shape. The characteristics of the PMFPSCS including its microstructure, sintering density and porosity are investigated. A uniaxial tensile test is carried out to study the tensile behaviors of the PMFPSCS. The deformation and failure mechanisms of the PMFSCS are discussed. Experimental results show that the PMFPSCS successively experiences an elastic stage, hardening stage, and fracture stage under tension. The tensile strength of the PMFPSCS is determined by a reticulated skeleton of fibers and reinforcement of copper powders. With the porosity of the PMFSS increasing, the tensile strength of the PMFPSCS decreases, whereas the reinforcement of copper powders increases. At the elastic stage, the structural elastic deformation is dominant, and at the hardening stage, the plastic deformation is composed of the structural deformation and the copper fibers' plastic deformation. The fracture of the PMFPSCS is mainly caused by the breaking of sintering joints.
Project description:In-situ dendrite/metallic glass matrix composites (MGMCs) with a composition of Ti₄₆Zr₂₀V₁₂Cu₅Be₁₇ exhibit ultimate tensile strength of 1510 MPa and fracture strain of about 7.6%. A tensile deformation model is established, based on the five-stage classification: (1) elastic-elastic, (2) elastic-plastic, (3) plastic-plastic (yield platform), (4) plastic-plastic (work hardening), and (5) plastic-plastic (softening) stages, analogous to the tensile behavior of common carbon steels. The constitutive relations strongly elucidate the tensile deformation mechanism. In parallel, the simulation results by a finite-element method (FEM) are in good agreement with the experimental findings and theoretical calculations. The present study gives a mathematical model to clarify the work-hardening behavior of dendrites and softening of the amorphous matrix. Furthermore, the model can be employed to simulate the tensile behavior of in-situ dendrite/MGMCs.
Project description:The sintering of metal powders is an efficient and versatile technique to fabricate porous metal elements such as filters, diffusers, and membranes. Neck formation between particles is, however, critical to tune the porosity and optimize mass transfer in order to minimize the densification process. In this work, macro-porous stainless steel (SS) hollow-fibers (HFs) were fabricated by the extrusion and sintering of a dope comprised, for the first time, of a bimodal mixture of SS powders. The SS particles of different sizes and shapes were mixed to increase the neck formation between the particles and control the densification process of the structure during sintering. The sintered HFs from particles of two different sizes were shown to be more mechanically stable at lower sintering temperature due to the increased neck area of the small particles sintered to the large ones. In addition, the sintered HFs made from particles of 10 and 44 ?m showed a smaller average pore size (<1 ?m) as compared to the micron-size pores of sintered HFs made from particles of 10 ?m only and those of 10 and 20 ?m. The novel HFs could be used in a range of applications, from filtration modules to electrochemical membrane reactors.
Project description:In this work, Ni particles/PA12 powders (Ni/PA12) and graphite oxide (GO)-encapsulated Ni particles/PA12 powders (GO-Ni/PA12) composite powders were prepared by defect-included electroless plating technique, and its laser sintered behaviour was investigated. Results showed that a lot of defects could formed on the surface of CH3COOH etched PA12 powders. The defects would induce Ni and GO-Ni particles independently plated on the PA12 surface. Adding GO in the plating solution would facilitate the deposition of Ni particles, GO, and NiO on the PA 12 surface, but inhibit the growth and the crystallinity of the Ni particles. The SLS process involved the contact of PA12 powders, the formation of sintering neck, the growth of sintering neck and the formation of fused solid. Sintering process could facilitate the re-arrangement of Ni particles due to surface tension and the growth of sintering neck. The Ni particles had well wettability, and the interfaces between Ni particles and PA 12 were contacted soundly. The tensile strength and bending strength of the 10 W-sintered Ni/PA12 specimen were 50?MPa and 60?MPa. But SLS process caused the serious aggregation of GO-Ni particles due to higher concentration, activity and surface area of GO-Ni particles.
Project description:The sintering behaviour of several green compacts made with olivine or olivine/alumina powder blends has been examined. To this goal, powders were attrition milled, uniaxially pressed into specimens and air sintered at temperatures ranging from 1100 to 1300 °C. The resulting samples were characterized by water absorption, shrinkage, phase composition and density. Compositions containing 5%, 10% and 20% Al₂O₃ have a sintering behaviour similar to that of olivine alone, reaching low residual porosity when fired at 1300 °C. Conversely, the composition containing 40% Al₂O₃ displays an almost flat shrinkage profile and maintains high residual porosity in the examined temperature range.
Project description:With regard to previous tensile deformation models simulating the tensile behavior of in-situ dendrite-reinforced metallic glass matrix composites (MGMCs) [Qiao et al., Acta Mater. 59 (2011) 4126; Sci. Rep. 3 (2013) 2816], some parameters, such as yielding strength of the dendrites and glass matrix, and the strain-hardening exponent of the dendrites, are estimated based on literatures. Here, Ti48Zr18V12Cu5Be17 MGMCs are investigated in order to improve the tensile deformation model and reveal the tensile deformation mechanisms. The tensile behavior of dendrites is obtained experimentally combining nano-indentation measurements and finite-element-method analysis for the first time, and those of the glass matrix and composites are obtained by tension. Besides, the tensile behavior of the MGMCs is divided into four stages: (1) elastic-elastic, (2) elastic-plastic, (3) plastic-plastic (work-hardening), and (4) plastic-plastic (softening). The respective constitutive relationships at different deformation stages are quantified. The calculated results coincide well with the experimental results. Thus, the improved model can be applied to clarify and predict the tensile behavior of the MGMCs.
Project description:The conventional soft solder used in soldering electronic joints is made up of 63% Sn and 37% Pb. It has been established that Pb is harmful to the body. Therefore, there is an on-going research to find a replacement for Pb. Al-Zn-Sn alloy is considered here as a possible replacement for soft solder of Sn and Pb. Three compositions of the alloy (Al-7Zn-3Sn, Al-10Zn-5Sn, and Al-13Zn-7Sn) were sintered at the sintering temperatures of 300 °C and 350 °C (and the constant pressure of 40 MPa, time of 5 mins, a heating rate of 20 °C/mins). Temperature/displacement/time variation data during the sintering were collected. The three alloys were compared after sintering by checking their microstructure, their densities, their hardness, their porosity, and their tensile strengths. Results showed that Al-13Zn-7Sn sintered at 350 °C, 40 MPa, 5 mins, 20 °C/mins had the highest densification of 99.7%, the lowest porosity of 0.3%, least hardness and strength of 450.34 MPa and 147.84 MPa respectively.
Project description:ZrCu-based bulk metallic glass composites (BMGCs) are well known for their plastic deformability, superior to traditional metallic glasses (MGs), which is attributed to a unique dual-phases structure, namely, the glassy matrix and unstable B2 phase. In the present study, in-situ tensile testing is used to trace the deformation process of a ZrCu-based BMGC. Three deformation stages of the BMGC, i.e., the elastic-elastic stage, the elastic-plastic stage, and the plastic-plastic stage are identified. In the elastic-elastic and elastic-plastic stages, the yield strength and elastic limit are major influenced by the volume fraction of the B2 crystals. In the plastic-plastic stage, the B2 phase stimulates the formation of multiple shear bands and deflects the direction of shear bands by disturbing the stress field in front of the crack tip. The deformation-induced martensitic transformation of the metastable B2 phase contributes to the plasticity and work hardening of the composite. This study highlights the formation and propagation of multiple shear bands and reveals the interactions of shear bands with structural heterogeneities in situ. Especially, the blocking of shear bands by crystals and the martensitic transformation of the B2 phase are critical for the mechanistic deformation process and illustrate the function of the B2 phase in the present BMGCs.
Project description:This work illustrates the effect of thermal mechanical processing parameters on the microstructure and mechanical properties of the Ti-22Al-25Nb alloy prepared by reactive sintering with element powders, consisting of O, B2 and Ti₃Al phases. Tensile and plane strain fracture toughness tests were carried out at room temperature to understand the mechanical behavior of the alloys and its correlation with the microstructural features characterized by scanning and transmission electron microscopy. The results show that the increased tensile strength (from 340 to 500 MPa) and elongation (from 3.6% to 4.2%) is due to the presence of lamellar O/B2 colony and needle-like O phase in B2 matrix in the as-processed Ti-22Al-25Nb alloys, as compared to the coarse lath O adjacent to B2 in the sintered alloys. Changes in morphologies of O phase improve the fracture toughness (KIC) of the sintered alloys from 7 to 15 MPa·m-1/2. Additionally, the fracture mechanism shifts from cleavage fracture in the as-sintered alloys to quasi-cleavage fracture in the as-processed alloys.
Project description:The ideal elastic limit is the upper bound to the stress and elastic strain a material can withstand. This intrinsic property has been widely studied for crystalline metals, both theoretically and experimentally. For metallic glasses, however, the ideal elastic limit remains poorly characterized and understood. Here we show that the elastic strain limit and the corresponding strength of submicron-sized metallic glass specimens are about twice as high as the already impressive elastic limit observed in bulk metallic glass samples, in line with model predictions of the ideal elastic limit of metallic glasses. We achieve this by employing an in situ transmission electron microscope tensile deformation technique. Furthermore, we propose an alternative mechanism for the apparent 'work hardening' behaviour observed in the tensile stress-strain curves.
Project description:Recently, with a broadening range of available materials and alteration of feeding processes, several extrusion-based 3D printing processes for metal materials have been developed. An emerging process is applicable for the fabrication of metal parts into electronics and composites. In this paper, some critical parameters of extrusion-based 3D printing processes were optimized by a series of experiments with a melting extrusion printer. The raw materials were copper powder and a thermoplastic organic binder system and the system included paraffin wax, low density polyethylene, and stearic acid (PW-LDPE-SA). The homogeneity and rheological behaviour of the raw materials, the strength of the green samples, and the hardness of the sintered samples were investigated. Moreover, the printing and sintering parameters were optimized with an orthogonal design method. The influence factors in regard to the ultimate tensile strength of the green samples can be described as follows: infill degree > raster angle > layer thickness. As for the sintering process, the major factor on hardness is sintering temperature, followed by holding time and heating rate. The highest hardness of the sintered samples was very close to the average hardness of commercially pure copper material. Generally, the extrusion-based printing process for producing metal materials is a promising strategy because it has some advantages over traditional approaches for cost, efficiency, and simplicity.