Effect of Cr Content on the Compression Properties and Abrasive Wear Behavior of the High-Volume Fraction(TiC–TiB_2)/Cu Composites

The(TiC–TiB2)/Cu composites with 50 vol% Ti C–Ti B2 ceramic particles were successfully fabricated by the combustion synthesis and hot press consolidation in a Cu–Ti–B4C–Cr system. The effects of the Cr content on the microstructures, hardness, compression properties, and abrasive wear behaviors of the composites were investigated. The final products consist of only Cu, Ti C, and Ti B2 phases, and the ceramic particles are distributed uniformly in these composites. The size of the ceramic particles decreases with Cr addition. As the Cr content increases, the yield strength,ultimate compression strength, microhardness, and abrasive wear resistance of the composites increase, and the fracture strain decreases.     

Effects of Forming Conditions and TiC–TiB_2 Contents on the Microstructures of Self-Propagating High-Temperature Synthesized NiAl–TiC–TiB_2 Composites

The NiAl–TiC–TiB2 composites were processed by self-propagating high-temperature synthesis(SHS) method using raw powders of Ni, Al, Ti, B4 C, TiC, and TiB2, and their microstructure and micro-hardness were investigated. The TiC–TiB2 in NiAl matrix, with contents from 10 to 30 wt%, emerged with the use of two methods: in situ formed and externally added. The results show that all final products are composed of three phases of NiAl, TiC, and TiB2. The microstructures of NiAl–TiC–TiB2 composites with in situ-formed TiC and TiB2 are fine, and all the three phases are distributed uniformly. The grains of NiAl matrix in the composites have been greatly refined, and the micro-hardness of NiAl increases from 381 HV100 to 779 HV100. However, the microstructures of NiAl–TiC–TiB2 composites with externally added TiC and TiB2 are coarse and inhomogeneous, with severe agglomeration of TiC and TiB2 particles. The samples containing externally added 30 wt% TiC–TiB2attain the micro-hardness of 485 HV100. The microstructure evolution and fracture mode of the two kinds of NiAl–TiC–TiB2 composites are different.     

Microstructure and strength of brazed joints of TiB2 cermet to TiAl-based alloys

In this study, TiB2 cermet and TiAl-based alloy are vacuum brazed successfully by using Ag-Cu-Ti filler metal.The microstructural analyses indicate that two reaction products, Ti ( Cu, Al ) 2 and Ag bused solid solution ( Ag ( s. s ) ) , are present in the brazing seam, and the iuterface structure of the brazed joint is TiB2/TiB2 Ag ( s. s ) /Ag ( s. s ) Ti ( Cu,Al)2/Ti( Cu, Al)2/TiAl. The experimental results show that the shear strength of the brazed TiB2/TiAl joints decreases us thebrazing time increases at a definite brazing temperature. When the joint is brazed at 1 223 K for 5 min, a joint strength up to 173 MPa is achieved.     

Effects of temperature on the mechanical properties of Ti6Al4V powder compacts prepared by magnetic pulse compaction

The effects of temperature (0-500°C) on the compressive strength,hardness,average relative density,and microstructure of Ti6Al4V powder green compacts prepared by magnetic pulse compaction were investigated.The results show that with increasing heating temperature,the compressive strength first increases and then decreases with the maximum value of 976.74 MPa at 400°C.The average relative density and hardness constantly increase,and their values reach 96.11% and HRA 69.8 at 500°C,respectively.The increase o...     

Effects of Joining Conditions on Microstructure and Mechanical Properties of C_f/Al Composites and TiAl Alloy Combustion Synthesis Joints

Cf/Al composites and TiAl alloy were joined by combustion synthesis in different joining conditions.Effects of additive Cu,joining temperature and holding time on joint microstructure and shear strength were characterized by employing DTA,SEM,EDS,XRD and shear test.Results show that the additive Cu in the Ti–Al–C interlayer could significantly decrease the reaction temperature owing to the emergence of Al–Cu eutectic liquid.Reaction degree of the interlayer was influenced by joining temperature and holding time.Due to the barrier action of formed TiAl3 layer,reaction rate of Ti and Al was determined by the atoms diffusion.The reaction between Ti and Al was more sensitive to the joining temperature rather the holding time.The joints shear strength was influenced by joining condition directly.The maximum shear strength of CS joints was 25.89 MPa at 600 °C for 30 min under 5 MPa.Interface evolution mechanism of the CS joint was analyzed based on the experimental results and phase diagram.     

Microstructure and properties of submicron-scale TiC particle reinforced titanium matrix composites prepared by shock wave consolidation

Submicron-scale TiC particle reinforced titanium matrix composites (TMCs) were prepared by shock wave consolidation technique at detonation speed of 2500-5000m/s. The microstructures were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The compressive strength and hardness values of the composites were also determined. The results show that the composites have higher compressive yield strength and hardness values than hot-rolled pure titanium. Twins in the microstructure of TMCs show that titani-um particles undergo plastic deformation during consolidation process. The fine grains with size less than 1 μm often locate in the boundaries among the titanium particles. TiC particles seem to keep unchanged during the consolida-tion. These bring about the increase in strength and hardness for the composites. The detonation speed of 3200 m/s is proper parameter for compacting powder in the present work.     

Characterization of diffusion-bonded joint between Al and Mg using a Ni interlayer

Aluminum and magnesium were joined through diffusion bonding using Ni interlayer. The microstructure and mechanical performance of the Al/Ni/Mg joints at different temperatures was investigated by means of scanning electron microscope(SEM), electro-probe microanalyzer(EPMA), X-ray diffraction(XRD), Vickers hardness testing, and shear testing. The results show that the addition of Ni interlayer eliminates the formation of Mg–Al intermetallic compounds and improves the bonding strength of the Al/Mg joints. The Al/Ni/Mg joints are formed by the diffusion of Al, Ni and Mg, Ni. The microstructure at the joint interface from Al side to Mg side is Al substrate/Al–Ni reaction layer/Ni interlayer/Mg–Ni reaction layer/Mg substrate multilayer structure. The microhardness of the Mg–Ni reaction layer has the largest value of HV 255.0 owing to the existence of Mg_2Ni phase.With the increase of bonding temperature, the shear strength of the joints increases firstly and then decreases.The Al/Ni/Mg joint bonds at 713 K for 90 min, exhibiting the maximum shear strength of 20.5 MPa, which is greater than that of bonding joint bonded directly or with Ag interlayer. The fracture of the joints takes place at the Mg–Ni interface rather than the Al–Ni interface, and the fracture way of the joints is brittle fracture.     

Effect of Zr addition on microstructures and mechanical properties of Ni-46Ti-4Al alloy

The microstructures and mechanical properties of Ni-(46-x)Ti-4Al-xZr (x = 0-8, at.%) alloys have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and mechanical tests. The results show that the Ni-Ti-Al-Zr alloys are composed of TiNi and (Ti, Al) 2 Ni with Zr as a solid solution element in both phases, and the third phase, (Zr, Ti, Al) 2 Ni, appears in Ni-40Ti-4Al-6Zr and Ni-38Ti-4Al-8Zr alloys. The compressive yield strength at room temperature increases with the increase of Zr content due to the solid-solution strengthening of Zr and precipitation strengthening of (Ti, Al, Zr) 2 Ni phase. However, the Ni-42Ti-4Al-4Zr alloy exhibits the maximum compressive yield strength at 873 and 973 K because of the softening of (Zr, Ti, Al) 2 Ni phase in the alloys with more Zr addition. The tensile stress-strain tests and the SEM fracture surface observations show that the brittle to ductile transition temperature of Ni-42Ti-4Al-4Zr alloy is between 873 and 923 K.     

Hot deformation behavior and microstructure evolution of TiC–Al_2O_3/Al composites

Hot compression behavior of TiC–Al2O3/Al composites was studied using the Gleeble-1500 system at a temperature range of 300–550 °C and at strain rate range of 0.01–10.00 s-1. The associated structural changes were studied by TEM observations. The results show that stress level decreases with deformation temperature increasing and strain rate decreasing, which can be represented by a Zener–Hollomon parameter in an exponent-type equation with hot deformation activation energy Q of 172.56 kJ·mol-1.Dynamic recovery occurs easily when strain rates are less than 10.00 s-1. Dynamic recrystallization can occur at strain rate of 10.00 s-1.     

Compressive Strength and Interface Microstructure of PCBN Grains Brazed with High-Frequency Induction Heating Method

In order to prepare monolayer brazed superabrasive wheels, the polycrystalline cubic boron nitride(PCBN)grains were brazed to AISI 1045 steel matrix with Ag–Cu–Ti filler alloy using the high-frequency induction heating technique. The compressive strengths of brazed grains were measured. Morphology, chemical composition and phase component of the brazing resultant around PCBN grain were also characterized. The results show that the maximum compressive strength of brazed grains is obtained in the case of brazing temperature of 965 °C, which does not decrease the original grain strength. Strong joining between Ag–Cu–Ti alloy and PCBN grains is dependent on the brazing resultants,such as TiB_2, TiN and AlTi_3, the formation mechanism of which is also discussed. Under the given experimental conditions, the optimum heating parameters were determined to be current magnitude of 24 A and scanning speed of0.5 mm/s. Finally, the brazing-induced residual tensile stress, which has a great influence on the grain fracture behavior in grinding, was determined through finite element analysis.     

Effect of carbon addition on microstructure and mechanical properties of Ti-based bulk metallic glass forming alloys

A kind of novel Ti-based composites was developed by introducing different amounts of carbon element to the Ti50 Cu23 Ni20 Sn7 bulk metallic glass forming alloys. The thermal stability and microstructural evolution of the composites were investigated. Room temperature compression tests reveal that the composite samples with 1% and 3% （mass fraction） carbon additions have higher fracture strength and obvious plastic strain of 2 195 MPa, 3. 1% and 1 913 MPa, 1.3% respectively, compared with those of the corresponding carbon-free Ti50 Ni20 Cu23 Sn7 alloys. The deformation mechanisms of the composites with improved mechanical properties were also discussed.     

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.     

Hot deformation behavior and microstructural evolution of powder metallurgical TiAl alloy

The hot deformation behavior of powder metallurgical(PM) TiAl alloys was investigated on Gleeble-3500 thermomechanical simulator, at a temperature range of 1050–1200 °C with an interval of 50 °C and a strain rate range of 0.001–1.000 s~(-1). The results show that the flow stress of PM TiAl alloy is sensitive to deformation temperature and strain rate, the peak stress decreases with the increase in deformation temperature and decrease in strain rate, and dynamic recrystallization occurs during the hot compression. The deformation active energy was calculated and the flow stress model during high-temperature deformation was established based on the Arrhenius equations and Zener–Hollomon parameter. The deformed microstructure consists of refined homogeneous γ and ɑ_2/γ grains.     

High-temperature mechanical properties of aluminium alloys reinforced with titanium diboride （TiB2） particles

The physical and mechanical properties of metal matrix composites were improved by the addition of reinforcements.The mechanical properties of particulate-reinforced metal-matrix composites based on aluminium alloys (6061 and 7015) at high temperatures were studied.Titanium diboride (TiB2) particles were used as the reinforcement.All the composites were produced by hot extrusion.The tensile properties and fracture characteristics of these materials were investigated at room temperature and at high temperatures to determine their ultimate strength and strain to failure.The fracture surface was analysed by scanning electron microscopy.TiB2 particles provide high stability of the aluminium alloys (6061 and 7015) in the fabrication process.An improvement in the mechanical behaviour was achieved by adding TiB2 particles as reinforcement in both the aluminium alloys.Adding TiB2 particles reduces the ductility of the aluminium alloys but does not change the microscopic mode of failure,and the fracture surface exhibits a ductile appearance with dimples formed by coalescence.     

Effect of Bonding Temperature on the Microstructures and Strengths of C/C Composite/GH3044 Alloy Joints by Partial Transient Liquid-Phase（PTLP） Bonding with Multiple Interlayers

With the use of Ti/Ni/Cu/Ni multiple foils as interlayer,carbon/carbon(C/C) composite was bonded to Nibased superalloy GH3044 by partial transient liquid-phase bonding technique.The effect of bonding temperature on the microstructures and strengths of the joints was investigated.The results showed that gradient structural multiple interlayers composed of ‘‘C–Ti reaction layer/Ti–Ni intermetallic compound layer/Ni–Cu sosoloid/residual Cu layer/Ni-GH3044 diffusion layer' were formed between C/C composite and GH3044.The shear strength of the C/C composite/GH3044 joint reached the highest value of 26.1 MPa when the bonding temperature was 1,030 °C.In addition,the fracture morphology showed that the fracture mode changed with the increase of bonding temperature.     

Mechanical Property of M40J_f/5A06Al Composite at Elevated Temperatures

In this work, aluminum alloy with a high concentration of magnesium(5A06) was reinforced with 55 vol% unidirectional ultra-high modulus and highly graphitized carbon fiber(M40J) using pressure infiltration method. The effect of temperature on the bending strength of the Cf/Al composites was investigated from room temperature to 500 ℃. The experimental results showed that the strength of M40Jf/5A06 Al composites was not affected by temperature from room temperature to 200 ℃. The bending strength of the composite at 300 ℃ was decreased by 30% compared with that at room temperature. In order to evaluate the extent of interface weakening, the length of fiber pullout was measured. The results showed that the pullout length reached the maximum at 300 and 500 ℃, which indicated weak interface at the corresponding temperature. The DSC curve presented obvious heat absorption peak at around 300 ℃, which may be attributed to the dissolution of the interfacial product b(Al3Mg2) phases at the C/Al interface. The bending fracture surfaces of the composites after three-point bending tests were observed by SEM, plastic-viscous flow of the matrix were observed at the samples tested at 500 ℃. The predominant mechanisms for high-temperature damage of M40Jf/5A06 Al composites are matrix softening caused by dislocation recovery and interface weakening caused by the dissolution of interfacial products.     

MICROSTRUCTURE AND COMPRESSIVE PROPERTIES OF NiAl-TiB_2 PARTICULATE COMPOSITES

Ni-50at.%Al matrix composites containing 0 to 20v.% TiB_2 particles have beensuccessfully fabricated by HPES technique. The results show that the Vickers hardness atroom temperature and the compressive yield strength from room temperature to 1000℃ ofthe composites increase with increasing volume.fraction of the strengthening phase. Espec-ially, the yield strength of NiAl-20TiB_2 was approximately twice as high as that ofunreinforced NiAl. The ductility of the composites at room temperature is also superior tothe monolithic NiAl.     

Preparation of High-Strength Al–Mg–Si/Al_2O_3 Composites with Lamellar Structures Using Freeze Casting and Pressureless Infiltration Techniques

Lamellar porous alumina scaffolds with the initial solid loadings of 20, 25, and 30 vol% were prepared by freeze casting using 5 lm alumina powders. With the addition of 3 wt% Mg O–Al2O3–Si O2 nanopowders in a eutectic composition as sintering aid, the maximum compressive strength of the sintered scaffolds reached(64 ± 2) MPa after sintering at 1,773 K for 2 h. The lamellar porous scaffolds were then filled with a molten Al–12Si–10 Mg alloy(in wt%)by pressureless infiltration at 1,223 K in a N2 atmosphere, yielding the shell-like structure of the composites. The compressive strength of the upper part composite with the initial 30 vol% solid loading reached(1,190 ± 50) MPa, which was about 3.5 times as large as that of the matrix alloy.     

Low-temperature heat conduction characteristics of diamond/Cu composite by pressure infiltration method

In this paper,diamond/CuCr and diamond/CuB composites were prepared using the pressure infiltration method.The physical property measurement system(PPMS)was adopted to evaluate the thermal conductivity of diamond/Cu and MoCu composites within the range of100–350 K,and a scanning electron microscope(SEM)was utilized to analyze the microstructure and fracture appearance of the materials.The research indicates that the thermal conductivity of diamond/Cu composite within the range of100–350 K is 2.5–3.0 times that of the existing MoCu material,and the low-temperature thermal conductivity of diamond/Cu composite presents an exponential relationship with the temperature.If B element was added to a Cu matrix and a low-temperature binder was used for prefabricated elements,favorable interfacial adhesion,relatively high interfacial thermal conductivity,and favorable low-temperature heat conduction characteristics would be apparent.     

Tribological properties of laser cladding TiB_2 particles reinforced Ni-base alloy composite coatings on aluminum alloy

To improve the wear resistance of aluminum alloy frictional parts, Ti B_2 particles reinforced Ni-base alloy composite coatings were prepared on aluminum alloy 7005 by laser cladding. The microstructure and tribological properties of the composite coatings were investigated. The results show that the composite coating contains the phases of Ni Al, Ni_3Al, Al_3Ni_2, TiB_2, TiB, TiC, CrB, and Cr_(23)C_6.Its microhardness is HV_(0.5)855.8, which is 15.4 % higher than that of the Ni-base alloy coating and is 6.7 times as high as that of the aluminum alloy. The friction coefficients of the composite coatings are reduced by 6.8 %–21.6 % and 13.2 %–32.4 % compared with those of the Ni-base alloy coatings and the aluminum alloys, while the wear losses are 27.4 %–43.2 % less than those of the Ni-base alloy coatings and are only 16.5 %–32.7 % of those of the aluminum alloys at different loads. At the light loads ranging from 3 to 6 N, the calculated maximum contact stress is smaller than the elastic limit contact stress. The wear mechanism of the composite coatings is micro-cutting wear, but changes into multi-plastic deformation wear at 9 N due to the higher calculated maximum contact stress than the elastic limit contact stress. As the loads increase to 12 N, the calculated flash temperature rises to 332.1 °C.The composite coating experiences multi-plastic deformation wear, micro-brittle fracture wear, and oxidative wear.