TiC-Maraging stainless steel composite： microstructure, mechanical and wear properties

Particulate TiC reinforced 17-4PH and 465 maraging stainless steel matrix composites were processed by conventional powder metallurgy （P/M）. TiC-maraging stainless steel composites with theoretical density 〉97% were produced using conventional P/M. The microstructure, and mechanical and wear properties of the composites were evaluated. The microstructure of the composites consisted of （core-rim structure） spherical and semi-spherical TiC particles depending on the wettability of the matrix with TiC particles. In TiC-maraging stainless steel composites, 465 stainless steel binder phase showed good wettability with TiC particles. Some microcracks appeared in the composites, indicating the presence of tensile stresses in the composites produced during sintering. The typical properties, hardness, and bend strength were reported for the composites. After heat treatment and aging, an increase in hardness was observed. The increase in hardness was at- tributed to the aging reaction in maraging stainless steel. The specific wear behavior of the composites strongly depends on the content of TiC particles and their interparticle spacing, and on the heat treatment of the maraging stainless steel.     

Enhanced mechanical properties in Al/diamond composites by Si addition

Diamond particles reinforced aluminum–silicon matrix composites,abbreviated as Al(Si)/diamond composites,were fabricated by squeeze casting.The effect of Si content on the microstructure and mechanical properties of the composites were investigated.The mechanical properties are found to increase monotonically with Si content increasing up to 7.0 wt%.The Al-7.0 wt% Si/diamond composite exhibits tensile strength of 78 MPa,bending strength of 230 MPa,and compressive strength of426 MPa.Al–Si eutectic phases are shown to connect with Al matrix and diamond particles tightly,which is responsible for the enhancement of mechanical properties in the Al(Si)/diamond composites.     

MICROSTRUCTURE AND PROPERTIES OF CuCr25 ALLOYS WITH DIFFERENT Ni CONTENT

CuCr25 alloys containing different Ni content were prepared by vacuum induction melting (VIM). The micro structure and properties were tested. The results show that with the increase of Ni content in CuCr25 alloys, the Cr phase changed from developed dendrite into nodular grains and was drastically refined; the electrical conductivity significantly decrease, but still reach the level of conventional CuCr50 when the Ni content is below 0.5%. The Ni content had little influence on their breakdown strength. The first breakdown sites transferred to the boundary of Cu and Cr phase for CuCr25Ni compared to the Cr phase for CuCr25 without Ni.     

Selective Laser Melting of In Situ TiB/Ti6Al4V Composites: Formability,Microstructure Evolution and Mechanical Performance

In the present study, a series of in situ TiB/Ti6Al4V composites were fabricated using selective laser melting. The formability, microstructure evolution and mechanical properties of the as-built samples added with different contents of TiB_2 were studied. It is found that the densification level is related to both the content of TiB_2 and laser energy density. The added TiB_2 reinforcement particle can spontaneously react with titanium and then form the TiB phase. The needle-like TiB phase tends to transform into dot-like particles with the decrease in energy density. Additionally, with the increase in TiB_2 content, the TiB phase is coarsened due to the increased nucleation rate and more reactions. The grain morphology is found to largely depend on the translational speed of solid–fluid interface determined by the temperature gradient and cooling rate. Also, the microhardness of the as-built TiB/Ti6Al4V composites is obviously improved. More interestingly, as the energy density increases, the microhardness of the as-built TiB/Ti6Al4V composites firstly increases and then decreases due to the synergy of grain size and different morphologies and distribution of TiB phases. The wear resistance of TiB/Ti6Al4V composites is far superior to that of Ti6Al4V alloy owing to the increased microhardness resulted from the uniform distribution of the hard TiB phase in the matrix.     

Microstructure and thermal properties of copper matrix composites reinforced with titanium-coated graphite fibers

Milled form of mesophase pitch-based graphite fibers were coated with a titanium layer using chemical vapor deposition technique and Ti-coated graphite fiber/Cu composites were fabricated by hot-pressing sintering. The composites were characterized with X-ray diffraction, scanning/transmission electron microscopies, and by mea-suring thermal properties, including thermal conductivity and coefficient of thermal expansion (CTE). The results show that the milled fibers are preferentially oriented in a plane perpendicular to the pressing direction, leading to anisotropic thermal properties of the composites. The Ti coating reacted with graphite fiber and formed a continuous and uniform TiC layer. This carbide layer establishes a good metallurgical interfacial bonding in the composites, which can improve the thermal properties effectively. When the fiber content ranges from 35 vol% to 50 vol%, the in-plane thermal conductivities of the composites increase from 383 to 407 Wá(máK) -1 , and the in-plane CTEs decrease from 9.5 9 10-6 to 6.3 9 10 -6 K-1 .     

Effect of Ti-Al on microstrucmres and mechanical properties of plasma arc in-situ welded joint of SiCp/A1 MMCs

The effect of Ti-Al on microstructures and mechanical properties of SiCp/Al MMC joints produced by plasma arc in-situ weld-alloying was investigated, in which argon-nitrogen mixture was used as plasma gases and Ti-Al alloy as filling composite. The results show that the formation of needle-like harmful phase Al4C3 is effectively prevented in the weld by in-situ weld-alloying/plasma arc welding with Ti-Al alloy sheet filler whose titanium content is more than 20%. The fluidity of molten pool is improved, and stable molten pool is gained for the addition of the Ti-A1 alloy. The mechanical properties of welded joint are effectively enhanced by the compact-grain structure and the new reinforced composites such as Al3Ti, TiN, AlN and TiC welded joint The test results of mechanical property show that the maximum tensile strength of welded joint gained by adding Ti-60Al alloy is up to 235 MPa. The factors influencing the tensile strength were also investigated.     

Aluminum-silicon carbide coatings by plasma spraying

An aluminum base composite (Al-SiC) powder has been developed for producing plasma sprayed coatings on Al and other metallic substrates. The composite powders were prepared by mechanical alloying of 6061 Al alloy with SiC particles. The concentration of SiC was varied between 20 and 75 vol%, and the size of the reinforcement was varied from 8 to 37 μm in the Al-50 vol% SiC composites. The 44 to 140 μm composite powders were sprayed using an axial feed plasma torch. Adhesion strength of the coatings to their substrates were found to decrease with increasing SiC content and with decreasing SiC particle sizes. The increase in the SiC content and decrease in particle size improved the erosive wear resistance of the coatings. The abrasive wear resistance was found to improve with the increase in SiC particle size and with the SiC content in the composite coatings.     

Influence of Deep Cryogenic Treatment on Microstructures and Mechanical Properties of an Ultrafine-Grained WC-12Co Cemented Carbide

Effect of deep cryogenic treatment(DCT) on the microstructures and mechanical behavior of ultrafine-grained WC-12 Co cemented carbide was investigated by using XRD, SEM, and DSC. The phase transformations of pure Co and binder phase Co in cemented carbide were analyzed in detail to correlate the strengthening mechanism with its a→ε phase transition. The results show that DCT resulted in a slight increase in hardness and bending strength of ultrafinegrained WC-12 Co cemented carbide. For the ultrafine-grained cemented carbide after DCT, there is no significant change in the microstructure and the elemental distribution of the cemented carbides, but the fractured morphology shows a feature of plastic deformation. In the cases of pure Co and the binder phase Co in WC-12 Co cemented carbide, they exhibit different features of phase transformation. The improvement of mechanical property of cemented carbide can be attributed to the increased amount of e-Co in WC-12 Co composites after DCT.     

Rheological model of semisolid Mg2Si/AM60 composites prepared by ultrasonic vibration treatment

The rheological behavior of semisolid Mg2 Si/AM60 composites prepared by ultrasonic vibration treatment was investigated.The effects of primary α-Mg solid content,the ultrasonic power and the content of reinforcement phase Mg2 Si on the apparent viscosity of semisolid composites were discussed.The results show that the apparent viscosity of the semis olid composites increases with the increase in a-Mg solid content.Meanwhile,the apparent viscosity decreases with the increase in ultrasonic power,...     

Characteristics of mechanical alloyed Ni-Al powder for sintering

Mechanical alloying was employed to obtain high-activity Ni-AI powder. The effects of mechanical alloying on the microstructure and characteristics of milled powder with a normal composition of Ni-22.89 at.% AI-0.5 at.% B were investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and transmission electron microscopy （TEM）. The results show that a solution Ni （AI） was obtained after milling. During mechanical alloying, the milled powder obtains extra surface energy and crystalline energy because the crystallite size becomes free and the lattice strain increases with the milling time prolonging. Furthermore, about 0.5 mol% oxide in the particles were formed after milling, and this kind of dis- persed oxide is effective to improve the properties of the sintered alloy by dispersion strengthening. It is confirmed that Ni3AI alloy with outstanding properties has been prepared with mechanical alloyed powders.     

Mechanical properties and expansion coefficient of Mo-Cu composites with different Ni contents

Mo-Cu composites were fabricated by powder metallurgy with addition of various Ni contents.The effect of Ni contents on mechanical and thermal properties of Mo-Cu composites was investigated.The results show that mechanical and thermal properties of Mo-Cu composites are greatly affected by the addition of Ni contents.The composite powders with Ni addition exhibits high sinterability.The sintering temperature is greatly decreased and the comprehensive properties of Mo-Cu composites are obviously improved.Mo-Cu composites with a content of 1.5 wt.％ Ni have relative density 99.2％,bending strength 1057.9 MPa,hardness 72.5 HRA,electronic resistivity 1.28× 10 -7Ω.m-1,thermal conductivity 139 W·m-1·K-1,and lower coefficient of thermal expansion 7.4×10-6 K 1.Mo-Cu composites have homogeneous and fine microstructure.The fracture mechanism is ductile fracture.     

Electrochemical properties of CeMgu Ni＋x% Ni composites （x=0, 50, 100 and 200） prepared by ball-milling

The electrochemical properties of the as-cast CeMg11 Ni and ball-milled CeMg11 Ni x%Ni(x=0, 50,100 and 200, mass fraction) composites were investigated. The results show that homogeneous amorphous phase of CeMg11 Ni x% Ni composite can be obtained by ball-milling, and discharge capacity of the ball-milled CeMg11 Ni x% Ni composites differs greatly depending on the amount of Ni introduced during milling. The CeMg11 Ni 200% Ni composite after 90 h ball-milling was found to exhibit a large discharge capacity of about 1 012 mAh/g at 303 K,and it also shows better charge-discharge cycling stability than those with lower Ni content. This remarkable improvement in electrochemical properties of the ball-milled composites seems to be attributed to the formation of an amorphous composite as well as the improvement of the surface state of the ball-milled particles.     

Effect of Bi on graphite morphology and mechanical properties of heavy section ductile cast iron

To improve the mechanical properties of heavy section ductile cast iron, bismuth （Bi） was introduced into the iron. Five castings with different Bi content from 0 to 0.014 wt.% were prepared; and four positions in the casting from the edge to the center, with different solidification cooling rates, were chosen for microstructure observation and mechanical properties test. The effect of the Bi content on the graphite morphology and mechanical properties of heavy section ductile cast iron were investigated. Results show that the tensile strength, elongation and impact toughness at different positions in the five castings decrease with a decrease in cooling rate. With an increase in Bi content, the graphite morphology and the mechanical properties at the same position are improved, and the improvement of mechanical properties is obvious when the Bi content is no higher than 0.011wt.%. But when the Bi content is further increased to 0.014wt.%, the improvement of mechanical properties is not obvious due to the increase of chunky graphite number and the aggregation of chunky graphite. With an increase in Bi content, the tensile fracture mechanism is changed from brittle to mixture ductile-brittle fracture.     

Effects of nano TiN addition on the microstructure and mechanical properties of TiC based steel bonded carbides

TiC based steel bonded carbides with the addition of nano TiN were prepared by vacuum sintering techniques.The microstructure was investigated using scanning electron microscopy（SEM） and transmission electron microscopy（TEM）,and the mechanical properties,such as bending strength,impact toughness,hardness,and density,were measured.The results indicate that the grain size becomes small and there is uniformity in the steel bonded carbide with nano addition;several smaller carbide particles are also found to be inlaid in the rim of the larger carbide grains and prevent the coalescence of TiC grains.The smaller and larger carbide grains joint firmly,and then the reduction of the average size of the grains leads to the increase in the mechanical properties of the steel bonded carbides with nano addition.But the mechanical properties do not increase monotonously with an increase in nano addition.When the nano TiN addition accounts for 6-8 wt.% of the amount of steel bonded carbides,the mechanical properties reach the maximum values and then decrease with further increase in nano TiN addition.     

Microstructure and Properties of In Situ Si and Fe-rich Particles Reinforced Al Matrix Composites Assisted with Ultrasonic Vibration

In this research, the in situ Si and Fe-rich particles reinforced Al matrix composites were fabricated by rheocasting(RC) process assisted with ultrasonic vibration(USV). After USV treatment, the polygonal primary Si crystals were refined into particles with average diameter of about 15–23 lm, and the fraction of primary Si declined to about5.4–6.5 vol%. The coarse plate-like d-Al4(Fe,Mn)Si2phase was transformed into fine particles with average diameter of about 17–20 lm, and the fraction of particle-like Fe-bearing particles is about 3.6–5.3 vol%. The ultimate tensile strength of the RC composites increases with the increase of Fe content at 350 °C. The increase of the elevated temperature strength of the composites is mainly attributed to the refinement of d-Al4(Fe,Mn)Si2phase and the increase of the volume fraction of the Fe-bearing compounds. Compared with the composites without USV, the RC composites assisted with USV have thinner mechanical mixing layer in wear test, which corresponds to smaller wear rate.     

Effect of rare earth La_2O_3 on the microstructure and mechanical properties of TiC/W composites

In this study, La2O3 was investigated as an additive to TiC/W composites. The composites were prepared by vacuum hot pressing, and the microstructure and mechanical properties of the composites were investigated. Experimental results show that the grain size of the TiC/W composites is reduced by TiC particles. When 0.5 wt.% La2O3 is added to the composites, the grain size is reduced further. According to TEM analysis, La2O3 can alleviate the aggregation of TiC particles. With La2O3 addition, the relative density of the TiC/W composites can be improved from 95.1% to 96.5%. The hardness and elastic modulus of the TiC/W 0.5 wt.% La2O3 composite are little improved, but the flexural strength and the fracture toughness increase to 796 MPa and 10.07 MPa·m1/2 respectively, which are higher than those of the TiC/W composites.     

Influence of Ce on microstructure and mechanical properties of LA141 alloys

LA141-（0-1.2）Ce alloys were prepared with vacuum induction melting method. The effects of Ce addition on the microstructure and mechanical properties of LA 141 alloys were studied. The microstructure and phases composition of these alloys were analyzed by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffractometry. The mechanical properties of these alloys were measured with tensile tester. The results show that Ce has refining effect on the alloys. In the alloys, some Al2Ce compounds exist, which make the A1 content dissolved in a and β phases decrease and the hard brittle Mg17Al12 phase refined. The refining effect improves the mechanical properties of alloys. When Ce content is 0.9%（mass fraction）, the tensile strength reaches 206.8 MPa and the elongation is two times as high as that of LAl41 alloy. Due to the generation of Al2Ce, the content of Al solid soluted in β phase decreases resulting in the decrease of alloy hardness with the addition of Ce.     

Effect of alloying elements on mechanical properties in Cu-15%Cr in-situ composites

The effects of alloying elements on the mechanical properties as well as electrical conductivity in Cu-15% (mass fraction) in-situ composites were systemalically studied and high strength and high electrical conductive Cu base in-situ composites have been developed. The best combination is the addition of 0.1% to 0.2% Zr, Ti, or Sn in Cu-15%Cr in-situ composite, thermomechanical treatment to refine the microstructure and optimizing the precipitation of second phase. The strength is controlled by high density of dislocations in the Cu matrix, the lamellar spacing of the second phase, and the fine Cr precipitates. The aging treatment to reduce solute atoms has a beneficial effect on the increase of electrical conductivity. The addition of Zr, or Ti of about 0. 15% to 0.2% promotes the precipitation of Cr particles.     

HA/Ti composite for biomedical application by mechanical milling

In order to overcome the poor mechanical properties of HA and the low bioactivity of Ti,HA/Ti composites with various compositions were prepared by mechanical milling.The effects of milling condition and the composition on the microstructure,the density and the hardness of the composites were studied.The results show that during the ball milling process.Ti particles are refined and the homogeneity of the HA/Ti mixtures is improved;HA will partially decompose due to the existence of Ti and high sintering temperature.The microstructure of HA/Ti composites is highly dependent on the milling condition and the composition.In the microstructure.Ti phase connects to be a continuous network,and HA/Ti mixtures disperse in the network.The longer the milling time,the finer the network will be.The density of HA/T composites decreases with the content of HA increasing and the milling time prolonging,because HA deteriorates the sinterability of Ti.The hardness of HA/Ti composites increases firstly with the content of HA increasing,and then drops when the content of HA exceeds 30%.Addition of HA will strengthen the HA/T composite but will decrease the density of the composite,which accounts for the effect of HA on the hardness of the composites.     

Mg alloy surface alloying layer fabricated through evaporative pattern casting technology

The influencing factors of surface alloying layer by evaporative pattern casting technology were investigated.A certain thickness alloying layer was formed on the surface of Mg-alloy matrix when the pouring temperature was 780°C with different vacuum degree and alloying powder size.The surface layer microstructure,micro area composition of the new phase formed on the matrix and the composition characteristics on the surface layer were examined by SEM and element scanning.The results show that the content of aluminum increases greatly on the surface layer.The micro-hardness of alloyed layer has a more obvious increase compared with that of the matrix.The size of alloying element and the vacuum degree are the key factors influencing the alloying layer,with the increase of element powder size from 0.074 to 0.15 mm and vacuum degree from 0.04 to 0.06 MPa,the surface alloying effect becomes better.