A study of mechanical properties and fractography of ZA-27/titanium-dioxide metal matrix composites

This paper reports an investigation of the mechanical properties and the fracture mechanism of ZA-27 alloy composites containing titanium-dioxide (TiO₂) particles 30–50 μm in size and in contents ranging from 0–6 wt.% in steps of 2 wt.%. The composites were fabricated by the compocasting technique. The results of the study revealed improvements in mechanical properties such as Young’s modulus, ultimate tensile strength, yield strength and hardness of the composites, but at the cost of ductility. The fracture behavior of the composites was influenced significantly by the presence of titanium dioxide particles. Crack propagation through the matrix and the reinforcing particles resulted in the final fracture. Scanning electron micrscopy (SEM) analyses were carried out to furnish suitable explanations for the observed phenomena.     

Microstructure and mechanical properties of hot-rolled Mg-Zn-Y-Zr magnesium alloy

Fine-grained magnesium alloys strengthened by quasicrystalline particles were easily developed by thermomechanical process for Mg-Zn-Y-Zr alloys. The microstructure evolution of Mg-Zn-Y-Zr alloys hot rolled with different reductions at different temperatures was studied. Tensile tests and fracture observation were carried out to study the mechanical properties of this alloy. The thin magnesium sheets hot rolled at 380 ℃ exhibit better combination of high strength and ductility than that hot rolled at lower temperature. The results show that the grains become equiaxed and uniform as compared with those of the extruded materials because of recrystallization and repeated heating between rolling passes. It is also found that with the increasing rolling temperature and strain the I-phase particles become much smaller and are homogeneously distributed in the matrix, which enhances both strength and ductility.     

Preparation and properties of PAn/ATTP/PE conductive composites

Polyaniline/Attapugite/PE（PAn-ATTP/PE）composites containing particles with core-shell structure were obtained via the two-step blending processs. The experimental condition is as follows： Organo-attapulgite and PAn was obtained by modifying attapulgite with laury benzenesulfonic acid sodium salt and, then added to PE. The electrical conductivity, structure and properties of the composites were studied. Under the function of shear stress, core-shell structure particles with ATTP as the core and PAn as the shell were formed in the composites. The structure of PAn-ATTP/PE composites were characterized by FTIR,XRD,SEM, etc, respectively. The effects of concentration of doping agent on the conductivity and mechanical property of the composites were investigated. The mechanical properties and impact fracture surface of the ternary composites were studied by means of the tensile tester, SEM, etc. The results show that polyaniline encapsulated ATTP enhances the strength of the PE. And the conductivity of PAn-ATTP/PE composites of is improved effectively when polyaniline encapsulated ATTP is added. The composite have good conductivity when 10% polyaniline encapsulated ATTP is added.     

Effect of extrusion on properties of Al-based composite

An aluminium alloy and its composite with dispersed SiC particles made by liquid metallurgy route were extruded under optimized conditions.The properties were characterized in terms of microstructure,hardness and sliding wear behaviour and then compared between the extruded and cast alloys and composites,in order to understand the benefits of composite and extrusion on the alloy.It was observed that composites drastically increased the hardness and the extruded composites further increased this value.The advantage of composites was realized in sliding wear tests.     

A Study of Mechanical Properties of the Iron-base Sintered Steel Adding Fine Cr-Fe Powder

This paper reports an investigation of the mechanical properties and the fracture mechanism of iron-based sintered alloy containing fine Cr-Fe powder particles 300 nm in size and in contents raging from 0.2-1.5 wt%. The iron-base alloy were sintered at 1120 ℃ for 40min. The results of the study revealed improvement in mechanical properties such as tensile strength, elongation and hardness of the sintered alloy. The fracture behaviors of the alloy were influenced significantly by the presence of Cr-Fe powder particles. The mechanical properties increased with increasing Cr content. Micrographs of fracture appeared dimple and quasi-cleavage.     

Mechanical Properties and Corrosion Behavior of Multi-Microalloying Mg Alloys Prepared by Adding AlCoCrFeNi Alloy

In this work, a series of multi-microalloying Mg alloys with a high degradation rate and high strength was prepared by adding AlCoCrFeNi HEA particles to the Mg melt followed by hot extrusion. The microstructure evolution and mechanical properties of the alloys were studied, meanwhile, the corrosion properties were evaluated by immersion weight loss and electrochemical tests. Results indicated that HEA particles in the Mg melt were decomposed and formed the Ni-rich phase,which was distributed un...     

Microstructural evolution and mechanical properties of in situ TiB2/Al composites under high-intensity ultrasound

Microstructural evolution and mechanical properties of in situ TiB2/Al composites fabricated with exothermic reaction process under high-intensity ultrasound produced by the magnetostrictive transducer were investigated. In this method, the microstructure and grain refining performance of the TiB2/Al composites were characterized by optical morphology(OM), scanning electron microscopy(SEM), energy-dispersive spectrometer(EDS), and X-ray diffraction(XRD) analysis.Microstructural observations show a decreasing trend in the grain size of the composites due to the ultrasound and the content of TiB2 particles in the composites. Compared with the process without ultrasound, the morphology and agglomeration of TiB2 particles are improved by high-intensity ultrasound. Meanwhile, it is proposed that the formation of TiB2 particles occurs via the transformation from Ti Al3, and at the optimal amount of the reactants, the conversion efficiency of Ti Al3 into TiB2 almost reaches up to 100 %. Finally, the effects of high-intensity ultrasound and TiB2 particles on the mechanical properties of the TiB2/Al composites were also discussed.     

Microstructure and Mechanical Properties of Mg–7.4% Al Alloy Matrix Composites Reinforced by Nanocrystalline Al–Ca Intermetallic Particles

Mg–7.6% Al(in mass fraction) alloy matrix composites reinforced with different volume fractions of nanocrystalline Al3Ca8 particles were synthesized by powder metallurgy,and the effect of the volume fraction of reinforcement on the mechanical properties was studied.Room temperature compression test reveals considerable improvement on mechanical properties as compared to unreinforced matrix.The compressive strength increases from 683 MPa for unreinforced alloy matrix to about 767 and 823 MPa for the samples having 20 and 40 vol% of reinforcement,respectively,while retaining appreciable plastic deformation ranging between 12 and 24%.The specific strength of the composites increased significantly,demonstrating the effectiveness of the low-density Al3Ca8 reinforcement.     

Microstructure evolution and mechanical properties of the Sip/Zn-Al composite joints by ultrasonic-assisted soldering in air

Hypereutectic Al-27 Si alloys were joined without flux by ultrasonic-assisted soldering at 420 ℃ in air using Zn-5 Al the filler alloys,and Si particulate-reinforced Zn-Al based composites filler joints were obtained. The ultrasonic vibration introduced into soldering could influence the migration of Si particles and the microstructure of solidified Zn-Al based alloys. Both the distribution of Si particles and microstructure of the solidified Zn-Al based alloys affected the shear strength of joints. The shear strength increased with the ultrasonic vibration time. The highest average shear strength of joints reached to ～ 68. 5 MPa. Transcrystalline rupture mode was observed on the fracture surface.     

Effects of yttrium on microstructure and mechanical properties of Mg-6Al magnesium alloy

Since Y has a great solid solubility in magnesium alloys, it helps enhancing the heat-resistant property of magnesium alloys. The effects of Y on microstructures and mechanical properties of Mg-6Al alloy have been studied in this work. The results show that Y addition refines grains of Mg-6Al alloy, and reduces the amount of the Mg 17 Al 12 phase. At the same time, the high melting-point Al 2 Y phase particles are formed. According to the mathematical model of the two-dimensional lattice misfit proposed by Braffit, it is believed that the Al 2 Y particles can serve as the nucleation sites for α-Mg. After T6 treatment, both elongation and ultimate tensile strength of Mg-6Al alloy at the room temperature and high-temperature increased firstly and then decreased, with increasing Y addition. The peak mechanical properties were achieved in the Mg-6Al-1.2Y alloy system. Y addition appears to change the fracture characteristic of Mg-6Al alloy. With 1.2wt%Y, the fracture surface of the alloy showed a lot of dimples and tearing ridges which connected the microscopic dimples and the fracture is mixed fracture of quasi-cleavage and ductile fracture.     

Pressureless Sintering of TiB<Subscript>2</Subscript>-B<Subscript>4</Subscript>C Ceramic Matrix Composite

The effect of TiB₂ addition on sinterability and mechanical properties of B₄C material was investigated. It was found that addition of TiB₂ aids the sintering process and permits pressureless sintering at temperatures between 2050 and 2150 °C. This also alleviates grain growth during sintering. The relative density reaches 98.5% of the theoretical density by increasing the percentage of TiB₂ in the composition. The mechanical properties such as hardness, fracture toughness, and bending strength were improved remarkably by addition of TiB₂.     

Fatigue crack growth resistance of SiC<Subscript>p</Subscript> reinforced Al alloys: Effects of particle size,particle volume fraction,and matrix strength

The main aim of this work was to study the effects of particle size, particle volume fraction, and matrix strength on the long fatigue crack growth resistance of two different grades of Al alloys (Al2124-T1 and Al6061-T1) reinforced with SiC particles. Basically, it was found that an increase in particle volume fraction and particle size increases the fatigue crack growth resistance at near threshold and Paris regimen, with matrix strength having a smaller effect. Near final failure, the stronger and more brittle composites are affected more by static modes of failure as the applied maximum stress intensity factor (K _max) approaches mode I plane strain fracture toughness (K _IC).     

Tribological Behavior of Aluminum Alloy AlSi10Mg-TiB<Subscript>2</Subscript> Composites Produced by Direct Metal Laser Sintering (DMLS)

Direct metal laser sintering (DMLS) is an additive manufacturing technique for the production of parts with complex geometry and it is especially appropriate for structural applications in aircraft and automotive industries. Aluminum-based metal matrix composites (MMCs) are promising materials for these applications because they are lightweight, ductile, and have a good strength-to-weight ratio This paper presents an investigation of microstructure, hardness, and tribological properties of AlSi10Mg alloy and AlSi10Mg alloy/TiB₂ composites prepared by DMLS. MMCs were realized with two different compositions: 10% wt. of microsize TiB₂, 1% wt. of nanosize TiB₂. Wear tests were performed using a pin-on-disk apparatus on the prepared samples. Performances of AlSi10Mg samples manufactured by DMLS were also compared with the results obtained on AlSi10Mg alloy samples made by casting. It was found that the composites displayed a lower coefficient of friction (COF), but in the case of microsize TiB₂ reinforcement the wear rate was higher than with nanosize reinforcements and aluminum alloy without reinforcement. AlSi10Mg obtained by DMLS showed a higher COF than AlSi10Mg obtained by casting, but the wear rate was higher in the latter case.     

Effects of ultrafine refractory carbides on microstructure and mechanical properties of hot-pressing sintered TiB2-ZrC cermet composites at different temperatures

TiB₂-ZrC cermet composites were sintered at different temperatures by hot pressing in vacuum. Effects of ultrafine refractory carbides and sintering temperatures on microstructures and mechanical properties were evaluated. The relationships between mechanical properties and microstructure are discussed. A typical black core-grey rim structure was observed; the grain size of TiB₂ remarkably decreased when ultrafine refractory carbides were added into the matrix. The incorporation of vanadium carbide (VC) and niobium carbide (NbC) clearly improved the flexural strength and hardness. This can be attributed to the fine uniform grain size and solid solution strengthening mechanism. It was also observed that the introduction of VC and tantalum carbide (TaC) enhanced the indentation fracture resistance of composites. This can be attributed to the favorable solubility of VC in TiB₂-ZrC system and the pinning effect of precipitated TaC. In this study, the typical core-rim structure, good solubility of VC, pinning effect of TaC, and crack deflection and branching improved the mechanical properties of TiB₂-ZrC cermet composites.     

激光熔覆B4C-TiO2-Al粉末制备原位TiB2+TiC/Fe复合涂层（英文）

采用B4C、TiO2、Al以及Fe基自熔合金粉末为前驱体,利用激光熔覆技术在钢基体上制备TiB2+TiC颗粒增强Fe基复合涂层。结果表明,激光熔覆过程通过B4C-TiO2-Al反应生成了均匀分布于基体的TiB2-TiC复合陶瓷相。TiB2颗粒呈长条块状,TiC以不规则形状分布于基体中。涂层具有比基材1045钢更好的耐磨性能,但涂层的摩擦因数小。     

Tensile and fracture toughness properties of SiC<Subscript>p</Subscript> reinforced Al alloys: Effects of particle size,particle volume fraction,and matrix strength

The goal of this work was to evaluate the effects of particle size, particle volume fraction, and matrix strength on the monotonic fracture properties of two different Al alloys, namely T1-Al2124 and T1-Al6061, reinforced with silicon carbide particles (SiC_p). From the tensile tests, an increase in particle volume fraction and/or matrix strength increased strength and decreased ductility. On the other hand, an increase in particle size reduced strength and increased the composite ductility. In fracture toughness tests, an increase in particle volume fraction reduced the toughness of the composites. An increase in matrix strength reduced both K _crit and δ_crit values. However, in terms of K _Q (5%) values, the Al6061 composite showed a value similar to the corresponding Al2124 composite. This was mainly attributed to premature yielding caused by the high ductility/low strength of the Al6061 matrix and the testpiece dimensions. The effect of particle size on the fracture toughness depends on the type of matrix and toughness parameter used. In general, an increase in particle size decreased the K _Q (5%) value, but simultaneously increased the amount of plastic strain that the matrix is capable of accommodating, increasing both δ_crit and K _crit values.     

Fracture mechanism of Ni3Al alloys and their composites with ceramic particles at elevated temperatures

Ni₃Al alloys and their matrix composites reinforced with fine ceramic particles have been successfully fabricated by reactive hot-pressing. This paper investigates the embrittlement mechanism of these materials at intermediate temperatures using a mechanical fracturing technique, i.e. a single edge chevron-notched beam method with variation of loading rate. In the case of monolithic alloys, extrinsic embrittlement originating from diffusion of atomic oxygen into plastic deformation zone coincides with the inherent brittleness connected with deterioration of grain boundary cohesion and unique dislocation motion at 673–1073 K. Oxygen embrittlement predominates over other mechanisms at 673 K, because significant loading rate dependence of fracture toughness is observed in air. The fracture toughness of the alloys intrinsically decreases at 873–1073 K. However, the mechanical behavior of their matrix composites is quite different, depending on the kind of reinforcement particles. Although the composites with TiN particles have high strength and ductility, their fracture toughness decreases at intermediate temperatures, in a similar manner to the monolithic alloys. The fracture toughness of TiC particle reinforced composites is exceptionally constant between 300 and 900 K.     

Tribological Properties of HVOF-Sprayed TiB<Subscript>2</Subscript>-NiCr Coatings with Agglomerated Feedstocks

Boride materials have drawn great attention in surface engineering field, owing to their high hardness and good wear resistance. In our previous work, a plasma-sprayed TiB₂-based cermet coating was deposited, but the coating toughness was significantly influenced by the formation of a brittle ternary phase (Ni₂₀Ti₃B₆) derived from the reaction between TiB₂ and metal binder. In order to suppress such a reaction occurred in the high-temperature spraying process, the high-velocity oxygen-fuel spraying technique was applied to prepare the TiB₂-NiCr coating. Emphasis was paid on the microstructure, the mechanical properties, and the sliding wearing performance of the coating. The result showed that the HVOF-sprayed coating mainly consisted of hard ceramic particles including TiB₂, CrB, and the binder phase. No evidence of Ni₂₀Ti₃B₆ phase was found in the coating. The mechanical properties of HVOF-sprayed TiB₂-NiCr coating were comparable to the conventional Cr₃C₂-NiCr coating. The frictional coefficient of the TiB₂-NiCr coating was lower than the Cr₃C₂-NiCr coating when sliding against a bearing steel ball.     

Relationship between microstructure,properties and reaction conditions for Cu–TiB2 alloys prepared by in situ reaction

Three Cu–TiB₂ alloys (0.45, 1.6, 2.5 wt.% TiB₂) have been prepared by a combination of in situ reaction and rapid solidification under optimized conditions. The relationship between microstructure, properties and in situ reaction condition for these Cu–TiB₂ alloys was investigated and analyzed by modeling. It is shown that the distribution and size of TiB₂ particles are strongly dependent on the choice of in situ reaction conditions and solute concentration; specifically, the size and aggregation level of TiB₂ particles tend to increase as the volume per cent of TiB₂ in the three Cu–TiB₂ alloys increases when the same in situ reaction conditions are used. The forming, coarsening and aggregation models of TiB₂ particles are established. The mechanical properties of three Cu–TiB₂ alloys are directly related to the distribution and size of TiB₂ particles, the change in the grain size and the residual solute concentration. A composite model reveals the separate contributions of these parameters to the mechanical properties.     

Effect of grain size on hot cracking resistance of the HAZ metal of welded joints in creep-resisting alloys

Summary

Al₂O₃/6061 aluminium alloy composite was welded to aluminium alloys (6061‐T6, 5052‐H14, 2017‐T4) using an inertia type friction welding machine to investigate the microstructures and hardness distributions of friction welded joints. Regardless of the aluminium alloys used, finer alumina particles and finer grain structures were observed in the area near the weld interface. And the occurrence of mechanical mixing and moving of alumina particles into a region other than the composite were observed clearly on the weld interface. The distance moved by the alumina particles became greater in the order of the alloys, 6061, 5052 and 2017. A softened area was observed in the heat affected zone of all the aluminium alloys. It was found 30 days after welding that the hardness of the welded joint between the composite alloy and 6061 alloy had not changed significantly, whilst that of the welded joint between the composite alloy and 2017 was observed to have recovered to the previous standard 14 days after welding.