Microstructure,interfacial reaction behavior,and mechanical properties of Ti_(3)AlC_(2)reinforced Al6061 composites

The interfacial reaction behavior of Al and Ti_(3)AlC_(2)at different pouring temperatures and its effect on the microstructure and mechanical properties of the composites were investigated.The results show that the addition of3.0 wt.%Ti_(3)AlC_(2)refines the average grain size ofα(Al)in the composite by 50.1%compared to Al6061 alloy.Morphological analyses indicate that an in-situ Al_(3Ti)transition layer of-180 nm in thickness is generated around the edge of Ti_(3)AlC_(2)at 720℃,forming a well-bonded Al-Al_(3Ti)interface.At this processing temperature,the ultimate tensile strength of A16061-3.0 wt.%Ti_(3)AlC_(2)composite is 199.2 MPa,an improvement of 41.5%over the Al6061 matrix.Mechanism analyses further elucidate that 720℃is favourable for forming the nano-sized transition layer at the Ti_(3)AlC_(2)edges.And,the thermal mismatch strengthening plays a dominant role in this state,with a strengthening contribution of about 74.8%.

Microstructure evolution,mechanical properties and fracture behavior of Al-xSi/AZ91D bimetallic composites prepared by a compound casting

In this paper,the effect of the Si content on microstructure evolution,mechanical properties,and fracture behavior of the Al-xSi/AZ91D bimetallic composites prepared by compound casting was investigated systematically.The obtained results showed that all the Al-xSi/AZ91D bimetallic composites had a metallurgical reaction layer(MRL),whose thickness increased with increasing Si content for the hypoeutectic Al-Si/AZ91D composites,while the hypereutectic Al-Si/AZ91D composites were opposite.The MRL included eutectic layer(E layer),intermetallic compound layer(IMC layer)and transition region layer(T layer).In the IMC layer,the hypereutectic Al-Si/AZ91D composites contained some Si solid solution and flocculent Mg_(2)Si+Al-Mg IMCs phases not presented in the hypoeutectic Al-Si/AZ91D composites.Besides,increasing Si content,the thickness proportion of the T layer increased,forming an inconsistent preferred orientation of the MRL.The shear strengths of the Al-xSi/AZ91D bimetallic composites enhanced with increasing Si content,and the Al-15Si/AZ91D composite obtained a maximum shear strength of 58.6 MPa,which was 73.4% higher than the Al-6Si/AZ91D composite.The fractures of the Al-xSi/AZ91D bimetallic composites transformed from the T layer into the E layer with the increase of the Si content.The improvement of the shear strength of the Al-xSi/AZ91D bimetallic composites was attributed to the synergistic action of the Mg_(2)Si particle reinforcement,the reduction of oxidizing inclusions and the ratio of Al-Mg IMCs as well as the orientation change of the MRL.

Effect of(Cr,V)_(2)(C,N)on the Microstructure and Mechanical Properties of WC-10Co Cemented Carbides

WC-10Co cemented carbides with finer WC and narrower grain size distributions are produced by using(Cr,V)_(2)(C,N)as grain growth inhibitors.As a result,with the increase of(Cr_(0.9),V_(0.1))_(2)(C,N)and(V_(0.9),Cr_(0.1))_(2)(C,N),the grains size of WC and mean free path of Co phase decrease,and adjacency of WC increases.Refinement and homogenization of grains enhance the transverse rupture strength(TRS)and the hardness.Meanwhile,the deflection and bridging of cracks keep the fracture toughness at a respectable level.The WC-10Co-0.6(Cr_(0.9),V_(0.1))_(2)(C,N)-0.025(V_(0.9),Cr_(0.1))_(2)(C,N)cemented carbides exhibit excellent comprehensive mechanical properties with the TRS of 4602.6 MPa,hardness of 1835 kg/mm^(2),and fracture toughness of 10.39 MPa·m^(1/2),respectively.However,the large pores are caused by excess N larger than 0.03 wt%and deteriorates the mechanical properties.We provide a new approach to WC-Co cemented carbides preparation with a narrow grain size distribution by adding novel grain growth inhibitors.

Microstructure and mechanical properties of stationary shoulder friction stir welding joint of 2A14-T62 aluminum alloy

2A14-T62 butt joint was successfully welded by stationary shoulder friction stir welding(SSFSW)method.The results showed that using a pin with small shoulder could broaden the process window,and under a rotation speed of 2000 r/min and welding speed of 30 mm/min,joint with smooth surface,small reduction in thickness and little inner defects was obtained.The weld nugget zone was approx-imately circular,which was a unique morphology for SSFSW.The heat-affected zone(HAZ)and thermo-mechanically affected zone(TMAZ)were both quite narrow due to the lower heat input and slight mechanical action of the stationary shoulder.The fraction of high angle grain boundaries(HAGBs)exhibited a“W”shape along horizontal direction(from advancing side to retreating side),and the minim-um value located at HAZ.The average ultimate tensile strength and elongation of the joint were 325 MPa and 4.5%,respectively,with the joint efficiency of 68.3%.The joint was ductile fractured and the fracture surface contained two types of dimples morphology in different re-gions of the joint.Microhardness distribution in the joint exhibited a“W”shape,and the difference along the thickness direction was negli-gible.The joint had strong stress corrosion cracking susceptibility,and the slow stain rate tensile strength was 139 MPa.Microcrack and Al2O3 particulates were observed at the fracture surface.

The aging behavior,microstructure and mechanical properties of AlN/AZ91 composite

Microstructure evolution and mechanical properties of the aging treated AlN/AZ91 composites were systematically investigated by optical microscopy(OM),high resolution scanning electron microscopy(HRSEM)with an energy dispersive spectrum(EDS),and high-angle annular dark field scanning transmission electron microscopy(HAADF-STEM).The results show that the higher fracture elongation(14±1%)and ultimate tensile strength(275±6 MPa)were simultaneously obtained in the peak-aged AlN/AZ91 composites.Comparied with AZ91 matrix alloy,the strength was increased by about 44%and the elongation was approximately five times higher,which mainly attributed to the precipitation of nano-sizedγ-Mg_(17)Al_(12)phase and the activation of non-basal slip systems induced by in-situ AlN particles at room temperature.However,the in-situ formation of AlN reinforcements consumed part of Al element in the matrix alloy,which resulted into the volume fraction decreasing ofγ-Mg_(17)Al_(12)precipitates,and then the age hardening and strengthening efficiency were reduced in the AlN/AZ91 composites.On the other hand,the mismatch of thermal expansion coefficient between AlN particles and AZ91 matrix generated high density dislocations around AlN particles,which promoted the precipitation ofγ-Mg_(17)Al_(12)phase,and then the peak aging time and temperature were decreased.

Microstructure and Mechanical Properties of ZrC_(x)-NbC_(y)-Cu Composites by Reactive Infiltration at 1300℃

ZrC_(x)-NbC_(y)-Cu composites were fabricated by pressure-less reactive infiltration of Zr-Cu binary melts into porous NbC preforms at 1300℃.The effect of Zr content in the infiltrator on microstructure of the as-synthesized composites was studied.Mechanical properties of the composites were reported.A partial displacement of Nb atoms in NbC by Zr atoms from Zr-Cu melt occurs during the reaction between Zr-Cu melt and porous NbC preform.The formation of a core-shell structure suggests the reaction is mainly a dissolutionprecipitation type.NbC dissolves into Zr-Cu melt,from which the(Nb,Zr)C_(z)phase precipitates and grows.With increasing Zr content in the Zr-Cu infiltrator,the reaction is enhanced and the infiltration is easily chocked.ZrC_(x)-NbC_(y)-Cu composite is synthesized using Zr_(14)Cu_(51)infiltrator.The flexural strength and fracture toughness of ZrC_(x)-NbC_(y)-Cu composite reach 637 MPa and 12.7 MPa·m^(1/2),respectively.And the improved toughness is probably attributed to residual Cu phase and plate-like Nb_(x)C_(y)phases.

Microstructure and mechanical properties of AZ31-Mg_2Si in situ composite fabricated by repetitive upsetting

AZ31-4.6% Mg2Si （mass fraction） composite was prepared by conventional casting method. Repetitive upsetting （RU） was applied to severely deforming the as-cast composite at 400 ℃ for 1, 3, and 5 passes. Finite element analysis of the material flow indicates that deformation concentrates in the bottom region of the sample after 1 pass, and much more uniform deformation is obtained after 5 passes. During multi-pass RU process, both dendritic and Chinese script type Mg2Si phases are broken up into smaller particles owing to the shear stress forced by the matrix. With the increasing number of RU passes, finer grain size and more homogeneous distribution of Mg2Si particles are obtained along with significant enhancement in both strength and ductility. AZ31-4.6%Mg2Si composite exhibits tensile strength of 284 MPa and elongation of 9.8%after 5 RU passes at 400 ℃ compared with the initial 128 MPa and 5.4%of original AZ31-4.6%Mg2Si composite.

Microstructure, mechanical properties and wear behaviour of Zn-Al-Cu-TiB_2 in situ composites

Zn-Al-Cu-TiB2（ZA27-TiB2） in situ composites were fabricated via reactions between molten aluminum and mixed halide salts（K2TiF6 and KBF4） at temperature of 875 °C. The microstructure, mechanical properties and wear behavior of the composites were investigated. Microstructure analysis shows that fine and clean TiB2 particles distribute uniformly through the matrix. The mechanical properties of the composites increase with the increase in TiB2 content. As TiB2 content increases to 5%（mass fraction）, an improvement of HB 18 in hardness and 49 MPa in ultimate tensile strength（UTS） is achieved. The overall results reveal that the composites possess low friction coefficients and the wear rate is reduced from 5.9×10-3 to 1.3×10-3 mm3/m after incorporating 5% TiB2. Friction coefficient and worn surface analysis indicate that there is a change in the wear mechanism in the initial stage of wear test after introducing in situ TiB2 particles into the matrix.

Microstructure and mechanical properties of (TiB+La_2O_3)/Ti composites heat treated at different temperatures

Near-α titanium matrix composites reinforced with TiB and La2O3 were synthesized by common casting and hot-working technology.The effects of β heat treatment temperature on the microstructure and the tensile properties of the in situ synthesized（TiB＋La2O3）/Ti were studied.Microstructure was studied by OM and TEM,and tensile tests were carried out at room temperature and 923 K,respectively.Results show that with the increase of β heat treatment temperature,prior β phase grain size increases and αcolony size decreases.Room temperature tensile strength increases with the increase of β heat treatment temperature,which can be attributed to the decrease of α colony size with the increase of β heat treatment temperature.However,high-temperature tensile strength decreases with the increase of β heat treatment temperature and the decrease of the high-temperature tensile strength is due to the increase of the prior β phase grain size.

Microstructure and mechanical properties of in situ TiB_2/7055 composites synthesized by direct magnetochemistry melt reaction

In situ TiB2/7055 composites were successfully synthesized via magnetic chemical direct melt reaction from 7055 （Al-3B）？Ti system. The phase composition and the microstructure of the composites were investigated by XRD, OM and SEM technologies, and the mechanical and wear properties were tested. The results indicate that with the pulsed magnetic field assistance, the morphologies of in situ TiB2 particles are mainly hexagonal-shape or nearly spherical, the sizes are less than 1 μm, and the distribution of the matrix is uniform. Compared the microstructures of the 7055 aluminum matrix composites synthesized without pulsed magnetic field, the average size ofα（Al） phase with pulsed magnetic field assistance is decreased from 20 to 10μm, the array of the second phase is changed from continuous net-shape to discontinuous shape. With the pulsed magnetic field, the tensile strengths of the composites are enhanced from 310 to 330 MPa, and the elongations are increased from 7.5%to 8.0%. In addition, compared with matrix alloy, the wear mass loss of the composites is decreased from 111 to 78 mg under a load of 100 N for 120 min.

Effect of applied pressure on microstructure and mechanical properties of Mg-Zn-Y quasicrystal-reinforced AZ91D magnesium matrix composites prepared by squeeze casting

The Mg-Zn-Y quasicrystal-reinforced AZ91 D magnesium matrix composites were prepared by squeeze casting process. The effects of applied pressure on microstructure and mechanical properties of the composites were investigated. The results show that squeeze casting process is an effective method to refine the grain. The composites are mainly composed of α-Mg, β-Mg17Al12 and Mg3Zn6Y icosahedral quasicrystal phase（I-phase）. With the increase of applied pressure, the contents of β-Mg17Al12 phase and Mg3Zn6 Y quasicrystal particles increase, further matrix grain refinement occurs and coarse dendritic α-Mg transforms into equiaxed grain structure. The composite exhibits the maximum ultimate tensile strength and elongation of 194.3 MPa and 9.2% respectively when the applied pressure is 100 MPa, and a lot of dimples appear on the tensile fractography. Strengthening mechanisms of quasicrystal-reinforced AZ91 D magnesium matrix composites are chiefly fine-grain strengthening and quasicrystal particles strengthening.

Effect of Zn addition on microstructure and mechanical properties of Mg-3Y-2Nd-0.5Zr alloy

The effect of 0.5wt.%Zn addition on the microstructure and mechanical properties of Mg-3Y-2Nd-0.5Zr(WE32)alloy was investigated.The results indicate that WE32-0.5Zn alloy takes 48 h to reach peak hardness after solid solution treatment at 525℃and aging at 200℃,10 h earlier than WE32 alloy,which implies an accelerated aging precipitation kinetics owing to the addition of 0.5wt.%Zn.A large quantity of finerod and rectangular block-like Zn-Zr precipitates in theα-Mg matrix are formed in the WE32-0.5Zn alloy,and numerous needle-likeβ1phases are distributed at both ends of the Zn-Zr precipitates at peak-aged condition.In peak-aged condition,the ultimate tensile strength considerably increases from 263.2 MPa(WE32)to 309.6 MPa(WE32-0.5Zn),and the elongation dramatically increases from 4.3%(WE32)to 8.9%(WE32-0.5Zn).Theβ’andβ1phases are the main precipitates of the WE32-0.5Zn alloy peak-aged at 200℃.Theβ’andβ1phases easily nucleate at the Zn-Zr precipitates,and theβ1phases are particularly likely to nucleate and grow at the interface between the two ends of the Zn-Zr precipitates,which accelerates aging precipitation kinetics and leads to a shorter time to achieve peak aging.

Microstructure and mechanical properties of GTA weldments of titanium matrix composites prepared with or without current pulsing

The effects of current pulsing on the microstructure, hardness and tensile properties at different temperatures of gas tungsten arc （GTA） weldments of titanium matrix composites were studied. Full-penetration butt joints were made with or without current pulsing. Optical microscopy, hardness test and scanning electron microscopy were employed to evaluate the metallurgical characteristics of welded joints. Tensile properties of weldments at different temperatures were studied and correlated with the microstructure. The results exhibit that current pulsing leads to the refinement of the weld microstrucmre and TiB whisker and the redistribution of reinforcements resulting in higher hardness, tensile strength and ductility of weldments in the as-welded condition.

Microstructure and mechanical properties of Ni-based composite coatings reinforced by in situ synthesized TiB_2 + TiC by laser cladding

A Ni-based composite coating reinforced by in situ synthesized TiB2 and TiC particles was fabricated on Ti6A14V by laser cladding. An attempt was made to correlate the thermodynamic predictions and experimental observation. The micro- structure and the microhardness profile across the coating were investigated by means of X-ray diffraction （XRD）, scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, and a hardness tester. It is found that the coating mainly consists of a large number of reinforcements （black blocky TiB2, flower-like or equiaxial TiC, and fine acicular CrB） and the 7 matrix. The hardness of TiB2, TiC, and CrB reinforcements is much higher than that of the 7 matrix. The dispersive distribu- tion of such high hardness reinforcements causes the increase in hardness of the whole coating. The average value of the hard- ness is approximately Hv0.2 700 in the coating. The hardness of the coating is obviously higher than that of the substrate due to the dispersion strengthening of reinforcements.

Mechanical Properties and Microstructure of In Situ TiB_2-7055 Composites

In order to fabricate a kind of high strength particulate reinforced aluminum-matrix composites, the high strength aluminum alloy 7055 was selected as a matrix. Composites reinforced with varying amounts of TiB2 particles were synthesized using the in situ method, and their mechanical properties and microstructure were analyzed. It is found that the in situ TiB2 particles sized from 50 to 400 um uniformly disperse in the matrix. With the weight fraction of TiB2 particles increasing, the elastic modulus as well as the yield strength and the ultimate tensile strength increase, while the ductility decrease. The improvement of strength could be attributed to good bonding between TiB2 and the matrix, and also the TiB2 particles act as a barrier to dislocation.

Microstructure and mechanical properties of ADC12 composites reinforced with graphene nanoplates prepared by ultrasonic assisted casting

Microstructure and mechanical properties of ADC12 composites reinforced with graphene nanoplates(GNPs)prepared by high-intensity ultrasonic assisted casting were investigated.The results indicated that high-intensity ultrasound can promote the uniform distribution of GNPs in the melt,resulting in refining theα(Al)phase and Si phase.The optimal addition of GNPs was 0.9 wt.%,and the optimal ultrasonic time was 12 min.The tensile strength,the yield strength and the hardness of the composite produced under the optimal parameters were 256.8 MPa,210.6 MPa and HV 126.0,respectively,which increased by 30.5%,42.7%,and 34.8%compared with those of the matrix,respectively.After adding the GNPs,the fracture mechanism gradually turned from a brittle fracture to a ductile fracture.The good interface and distribution allowed GNPs to play the role in fine grain strengthening,dislocation strengthening and load transfer strengthening effectively.

Microstructures and mechanical properties of Al 2519 matrix composites reinforced with Ti-coated SiC particles

Ti-coated SiCp particles were developed by vacuum evaporation with Ti to improve the interfacial bonding of SiCp/Al composites.Ti-coated SiC particles and uncoated SiC particles reinforced Al 2519 matrix composites were prepared by hot pressing,hot extrusion and heat treatment.The influence of Ti coating on microstructure and mechanical properties of the composites was analyzed by scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS).The results show that the densely deposited Ti coating reacts with SiC particles to form TiC and Ti5Si3 phases at the interface.Ti-coated SiC particle reinforced composite exhibits uniformity and compactness compared to the composite reinforced with uncoated SiC particles.The microstructure,relative density and mechanical properties of the composite are significantly improved.When the volume fraction is 15%,the hardness,fracture strain and tensile strength of the SiCp reinforced Al 2519 composite after Ti plating are optimized,which are HB 138.5,4.02%and 455 MPa,respectively.

MICROSTRUCTURES AND MECHANICAL PROPERTIES OF IN-SITU Al_2O_3/TiAl COMPOSITES BY EXOTHERMIC DISPERSION METHOD

In-situ Al2O3/TiAl composites were fabricated by pressure-assisted exothermic dispersion （PAXD） method from elemental powder mixtures of Ti, Al, TiO2, and Nb2O5. The microstructures and mechanical properties of the as-sintered composites are investigated. The results show that the as-sintered products consist of γ-TiAl, α2-Ti3Al, Al2O3, and NbAl3 phases. Microstructure analysis indicates that Al2O3 particles tend to disperse on the grain boundaries. Application of a moderate pressure of 35 MPa at 1200℃ yields Al2O3/TiAl composites with fine Al2O3 reinforcement and a discontinuous network linking by Al2O3 particles. The aluminide component has a fine submicron γ ＋α2 lamellar microstructure. With increasing Nb2O5 content, Al2O3 particles are dispersed uniformly in the matrix. The hardness of the composites increases gradually, and the bending strength and fracture toughness of the composites reach to the maximum value, respectively.

Microstructure and mechanical properties of WC-20wt% Co/ZrO_2(3Y)cermet composites

The cermet composites WC-20wt%Co/ZrO2（E6）with four different comtents of ZrO2（3Y）were prepared by normal vacuum sinter processing;the optical microscope and SEMwere used to characterize their microstructures.The hardness.bending strength and impact toughness of the specimens were determined.The experimental results show that ZrO2（3Y） particles in WC-20wt%Co matrix are sphcrical particles in different sizes which are distributed uniformly in Co phases and WC phases,the bending strength and impact toughness of the WC-20wt%Co cermet composites added ZrO2（3Y）improve remarkably.but the hardness values have little change.

Microstructure and mechanical properties of B_4C-TiB_2-Al composites fabricated by vacuum infiltration

B4C-TiB2-Al composites were fabricated by infiltrating aluminum into porous B4C-TiB2 preforms in vacuum. The microstucture and mechanical properties of the B4C-TiB2-Al composites were investigated. The hardness decreased, the flexural strength increased, and the fracture toughness first increased and then decreased slightly with an increase in TiB2 content. The BaC-TiB2-Al composite with 40wt.% TiB2 showed the optimized properties. The infiltrated aluminum addition was the leading reason for the fracture toughness improvement of the composites. The tear ridges and dimples on the fracture surface of the composites increased gradually with the increase of infdtrated alu- minum content showing inter/transgranular fracture mode. The relationships between the microstructures and the mechanical properties of the composites were discussed.