Two-step sintering of TiB2–40wt%TiN composites

Two-step pressureless sintering was investigated for TiB₂–40wt%TiN system. The calculation for phase equilibria was performed, which indicates that a significant nitrogen loss can occur at 1700 °C while ZrO₂ readily dissolves into TiN lattice from 1600 °C. The XRD analysis revealed that nitrogen loss was greater during first step at low temperature but smaller for second step at high temperature. As a result, the high-temperature processing of the second step provided better densification and mechanical properties than those of one-step sintering.     

Combustion synthesis of FeAl−Al2O3 composites with TiB2 and TiC additions via metallothermic reduction of Fe2O3 and TiO2

Combustion synthesis involving metallothermic reduction of Fe₂O₃ and TiO₂ was conducted in the mode of self-propagating high-temperature synthesis (SHS) to fabricate FeAl-based composites with dual ceramic phases, TiB₂/Al₂O₃ and TiC/Al₂O₃. The reactant mixture included thermite reagents of 0.6Fe₂O₃+0.6TiO₂+2Al, and elemental Fe, Al, boron, and carbon powders. The formation of xFeAl−0.6TiB₂−Al₂O₃ composites with x=2.0−3.6 and yFeAl−0.6TiC−Al₂O₃ composites with y=1.8−2.75 was studied. The increase of FeAl causes a decrease in the reaction exothermicity, thus resulting in the existence of flammability limits of x=3.6 and y=2.75 for the SHS reactions. Based on combustion wave kinetics, the activation energies of E_a=97.1 and 101.1 kJ/mol are deduced for the metallothermic SHS reactions. XRD analyses confirm in situ formation of FeAl/TiB₂/Al₂O₃ and FeAl/TiC/Al₂O₃ composites. SEM micrographs exhibit that FeAl is formed with a dense polycrystalline structure, and the ceramic phases, TiB₂, TiC, and Al₂O₃, are micro-sized discrete particles. The synthesized FeAl−TiB₂−Al₂O₃ and FeAl−TiC−Al₂O₃ composites exhibit the hardness ranging from 12.8 to 16.6 GPa and fracture toughness from 7.93 to 9.84 MPa·m^1/2.     

Microstructure and properties of Fe–Cr–C hardfacing alloys reinforced with TiC–TiB2

Abstract

Different amounts of TiB₂ powder were added to flux cores of wear resistant hardfacing flux cored wires for the preparation of new flux cored wires. Fe–Cr–C hardfacing alloys reinforced with TiB₂ were produced by arc hardfacing. The microstructure, hardness and wear resistance behaviour of the hardfacing alloys were investigated using an optical micrograph, scanning electron micrograph (SEM), X-ray diffractometer, macrohardness tester, microhardness tester and abrasive wear tester. The results showed that, among the hardfacing alloys, a new hard phase, i.e. TiC–TiB₂ composite compound particles, was formed and dispersed in the primary carbides and matrix structures. The TiC–TiB₂ reinforced Fe–Cr–C hardfacing alloys imparted greater hardness and better wear resistance. The presence of TiC–TiB₂ hard phase particles is the main reason for the improvement in hardness and wear resistance of Fe–Cr–C hardfacing alloys.     

High-temperature compressive properties of TiC–TiB_2/Cu composites prepared by self-propagating high-temperature synthesis

TiC–TiB2 /Cu composites were prepared by self-propagating high-temperature synthesis with pseudo hot isostatic pressing using Ti, B4 C, and Cu powders. The compressive deformation of the composites at high temperature was investigated. It is found that the maximum compressive strength decreases with the increase of temperature and Cu content. The deformation of the composites includes the steps of elastic, stable rheology, and inaction. The maximum strain is in the range of 5 %–10 %. Before fracture, TiC–TiB2 /40Cu becomes drum-shaped at 1123 K; however, TiC–TiB2 /20Cu only has a brittle fracture along the axial direction of 45°. The results show that the compressive strength of TiC–TiB2 /Cu decreases from 823 to 1223 K. However, the maximum compressive strength of TiC–TiB2 /20Cu reaches 1850 MPa at 823 K, which predicts that this series of composites could be applied to high-temperature compressive materials.     

Microstructural,thermal and mechanical characterization of TiB2–SiC composites doped with short carbon fibers

Spark plasma sintering method, at the temperature of 1800 °C under the pressure of 40 MPa for 7 min, was employed for fabrication of TiB₂–SiC-based composites. The influences of short carbon fiber (C_f) addition (2 wt%) on microstructural, mechanical and thermal properties of TiB₂–SiC ceramics were studied. Carbon fiber addition increased the relative density of sintered composite which observed to have direct effect on mechanical and thermal properties. The mechanical properties of composites were measured by nanoindentation method. Hardness and elastic modulus of TiB₂/SiC interfaces in carbon fiber doped composite were measured 27.1 GPa and 445 GPa, respectively, while these values were obtained 24.2 GPa and 422 GPa for carbon-free sample. The thermal diffusivity of samples was measured by laser flash technique (LFT). It was found that TiB₂–SiC–C_f composite has a higher thermal conductivity (55 w/m.K) compared to TiB₂–SiC ceramic with a value of 54.8 w/m.K.     

Thermal explosion synthesis of aluminum matrix composites reinforced with TiC-TiB2 ceramic particulates

In situ TiC-TiB2 diphase ceramic reinforced aluminum metal matrix composites were successfully fabricated via thermal explosion （TE） reaction in the Al-Ti-B4C system, Using DTA and XRD analyses, the combustion reaction characteristic was examined. The results show that Al serves not only as a diluent but also as a reaction participant, affecting the reaction process and its final products. Combining with the DTA and the TE temperature-time curves, the ignition temperature is estimated to be about 970 K. With increasing Al content, the adiabatic combustion temperature is lowered and the sizes of the TiC and TiB2 particulates decrease. When the Al content in the reactants is more than 50%, AlaTi intermediate phase is detected in the synthesized products. SEM observations reveal that the nearly spherical TiC particles and hexagonal or rectangular TiB2 particles distribute relatively uniformly in the Al matrix.     

Effect of Cu element on morphology of TiB2 particles in TiB2/Al−Cu composites

In order to explore the influence of Cu element on the morphology evolution of the in-situ TiB₂ particles, the 10 wt.% TiB₂ reinforced Al−5wt.%Cu based composite was prepared by mixed salt casting. The morphology characterization and transformation of TiB₂ reinforcements caused by Cu element were investigated by multi-scale microstructure characterization and statistics techniques. In the case of controlled casting, 5 wt.% Cu addition was found to transform the TiB₂ particle morphology from hexagonal plate with sharp edges and corners to hexagonal or tetragonal prism with chamfered edges and corners with the distinguishing growth steps both on the top surface and the side surface. The TiB₂ growth in Al−Cu matrix followed the rules: nano-scaled spherical nuclei—polyhedron grains—chamfered hexagonal particles—hexagonal plates—chamfered particles with obvious growth steps. The adsorption energy of Cu on different crystal surfaces of TiB₂ was caculated to reveal the influence mechanism and the results indicated that Cu was preferentially adsorbed on the (101(—)1)_TiB2 crystal planes, devoting to the small aspect ratio of TiB₂.     

Self-propagating high temperature synthesis of MoSi2 matrix composites

MoSi2 is presently regarded as the most important material for electrical heating and as one with huge potential for high temperature structural uses. MoSi2 and MoSi2 matrix composites were prepared by self-propagating high temperature synthesis （SHS）. Pure MoSi2 was obtained and a compound of MoSi2 and WSi2was synthesized in the form of predominant solid solution （Mo,W）Si2. By adding aluminum of 5.5 at.% to Mo-Si, the crystal structure of MoSi2 changed into a mixture of tetragonal Cllb MoSi2and hexagonal C40 Mo（Si,Al）2. The （Mo,W）Si2-Mo（Si,Al）2-W（Si,Al）2 composite materials were synthesized by adding aluminum of 5.5 at.% to Mo-W-Si. However, if the amount of the added aluminum was not larger than 2.5 at.%, it did not have any significant effect. SHS is an effective technology for synthesis of MoSi2 and MoSi2 matrix composites.     

Selective Laser Melting process optimization of Ti–Mo–TiC metal matrix composites

Selective Laser Melting (SLM) was used to process a powder mixture of CP Ti, 6.5 wt% Mo and 3.5 wt% Mo₂C. The process parameters were optimized to obtain full-density, crack free parts. After the in situ decomposition of Mo₂C in favor of the formation of TiC, the material consisted of a homogeneous dispersion of submicrometer sized TiC platelets in a β-(Ti,Mo) matrix exhibiting a high hardness up to 550 HV and compressive yield stress of 1164 ± 37 MPa. The microstructure and mechanical properties could be tailored by variation of the process parameters within the high-density processing window, as well as through post-process heat treatments.     

Failure of metal–ceramic composites with spherical inclusions

In this work the development of cavities in spherical metal inclusions within a metal–ceramic composite and the subsequent influence upon the strength of the composite is investigated. A model experiment is undertaken whereby 100 μm diameter spherical aluminium inclusions are placed within an Al₂O₃–Al interpenetrating network composite. The samples are then fractured at temperatures ranging from room temperature to just below the melting temperature of aluminium. It is found that fracture originates from the aluminium inclusions and that there is clear evidence of cavitation in the ductile inclusions which also shows that these cavities formed as a result of high triaxial stress during cooling as a part of the fabrication process. This observation is supported by a numerical model of the stress formation and cavity growth process within an inclusion during cooling. The model also provides information on the effect of initial cavity size and location. Comparisons of experimental fracture strength and toughness data indicate that the observed high strength of these composites is explained by crack growth resistance due to ductile ligament bridging.     

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.     

TiB2—TiC和TiB2—SiC陶瓷复合材料的活化烧结

TiC、TiB2和SiC都具有许多非常重要的性能，其中包括强耐磨性、高熔点、高硬度和良好的化学稳定性．加入第二相能够提高碳化物陶瓷的强度和韧性．往SiC基体内添加TiB2或者TiC粒子就能够大大提高SiC制品的断裂韧性，SiC含量高的材料用于生产耐磨和耐蚀制品，而TiC和TiB2含量高的材料则在电子技术方面具有广阔的前景．俄罗斯莫斯科罗蒙诺夫精微化学工艺研究所（MNTXY）的彼得洛夫和．列文斯基指出，目前这些复合材料尚未得到广泛的工业普及，原因是由担本混合物（热压坯料）制取致富产品的成本高和韧性低．在烧结这些材料时，扩散一…     

In-situ synthesis and characterization of Fe – TiC based cermet produced from enhanced carbothermally reduced ilmenite

In-situ synthesis of Fe-TiC based cermet by carbothermic reduction of South African ilmenite ore has been successfully achieved. This was carried out in an argon containing atmosphere in the temperature range of 850–1350 °C. Powder mixtures of ilmenite concentrate and graphite in molar ratio of 1:4 respectively, were milled for 2 h in a planetary mill (PM 100) to obtain intimate mixtures. The mixtures were then synthesized in a laboratory high temperature furnace at different reduction temperatures. The obtained X-ray diffraction results showed that Fe-TiC has been successfully formed at 1350 °C with 15 min holding time. The sequence of phase evolution showed a stepwise reduction of ilmenite FeTiO₃ initially to form a mixture of Fe and TiO₂, which was successively further reduced to Ti₄O₇, Ti₃O₅, Ti₂O₃ and finally TiC. Three or more major peaks were observed from thermo-analyses (TG, DTG and DTA) corresponding to the initial reduction of FeTiO₃ at 983.3 °C, Ti₄O₇ at 1050 °C, Ti₃O₅ at 1200 °C and finally TiC at 1350 °C. Field Emission SEM coupled with elemental analysis showed a clear phase boundary between the metallic phase (Fe) and the ceramic –TiC in the cermet synthesized at 1350 °C.     

Formation of TiC/Ti2AlC and α2+γ in in-situ TiAl composites with different solidification paths

In order to improve the mechanical properties of TiAl alloys, TiAl composites with different solidification paths were synthesized by metallurgical method. Results show the TiC disappears and Ti₂AlC increases when the Al content is more than 42% (at.%, similarly hereinafter). Small TiC particles are located in Ti₂AlC grains with irregular shapes when the Al content is 40%, and they translate into clubbed Ti₂AlC with increasing of Al. This metallurgy method can solve the defects of the Al lacking and the residual TiC. The γ phase increases between lamellar colonies with the increasing of Al. When the Al content is 48%, the fully lamellar structure transforms into a duplex microstructure and there are small Ti₂AlC phases in γ phases, because the forming of Ti₂AlC phase must consume Al. The compressive strength increases up to 1678.68 MPa as Al content is 46 at.%, and then decrease to 1460.22 MPa, the compressive strain increases and then keeps stabilization with the increasing Al. The maximum strength improves 38.82% and the maximum strain improves 121.37%. The Ti₂AlC/TiAl composites fracture behaviors are load transferring behavior, crack deflection, trans-lamellar cracking and extraction of carbide reinforcements. The Ti₂AlC phase and the fully lamellar structure improve the mechanical properties.     

Role of nano-WC addition on microstructural,mechanical and thermal characteristics of TiC–SiCw composites

In this research, various amounts of nano-sized tungsten carbide (WC_n: 0, 1.5, and 3 wt%) were added to TiC-10 vol% SiC_w system. All samples were sintered at 1900 °C under an external pressure of 40 MPa for 7 min by spark plasma sintering (SPS) procedure. Microstructural, thermodynamical, and XRD evaluations revealed the formation of non-stoichiometric TiC_x, in-situ TiC, SiC, and WSi₂. The carbon exited the TiC lattice owing to the formation of non-stoichiometric TiC_x precipitated at the grain boundaries. Although introducing 1.5 wt% WC_n enhanced the relative density of TiC-SiC_w (98.7%) by around 0.7%, further addition of this sintering aid had a destructive impact. The addition of WC_n decreased both hardness and flexural strength of the specimens, and the poorest values (11.6 GPa and 368 MPa, respectively) were recorded for TiC-10 vol% SiC_w-3 wt% WC_n. The highest thermal conductivity (24.3 W/m.K) was obtained by the addition of 1.5 wt% WC_n.     

Fabrication and mechanical properties of FeAl/TiC composites

1　INTRODUCTIONOver the past few decades, considerable inves tigations have been carried out to identify alterna tive binders for cermets in order to improve theirmechanical properties and also to overcome certainshortcomings, such as high cost and density, lowoxidation and corrosion resistance, and environ mental toxicity[1, 2]. Iron aluminides are of particu lar interest due to their low cost and density, highspecific strength, environmental friendliness andexcellent oxidati…     

Fabrication and mechanical properties of FeAi／TiC composites

FeAl/TiC composites were fabricated by reactive hot pressing blended elemental powders. The effects of TiC content, composition of the binder phase and Ni alloying on the densification process and mechanical properties of the composites were studied. The results show that the densities of the composites decrease with the increase of TiC content. Closely related with their porosities and flaw densities, the hardness and bend strength of the composites show peak values with the increase of TiC content. Higher content of Al in the binder phase was beneficial to densification, however it deteriorates the mechanical properties of the composites. The addition of Ni significantly improves the densities of the composites by enhancing matter transfer in the binder phase. By alloying with Ni, the mechanical properties of the composites are greatly improved due to the increase of the density, together with solid solution-strengthening the binder phase and promoting ductile fracture of FeA1.     

Reaction mechanism and microstructure development of strain tolerant in situ SiC–BN composites

The reaction mechanism and microstructure development of strain tolerant in situ SiC–BN composites fabricated from the in situ reaction of Si₃N₄, B₄C and C were investigated. This exothermic reaction took place at about 1400°C in an argon atmosphere according to the results of X-ray diffraction analysis and differential thermal analysis. The reaction finished after hot pressing at 1700°C for 60 min, and densification occurred mainly in the temperature range of 1700°C to 2000°C. In spite of poor sinterability of BN, composites with rather high density were obtained. Chemical composition analysis of the composites obtained showed that there was no obvious change in the composition after hot pressing. The in situ formed SiC was of the β-type with a quasi-spherical shape, whereas the in situ BN was graphitic hexagonal with a flake shape, and was located at the grain boundaries of SiC. The composite obtained showed a very fine and homogeneous microstructure. The bending strength of the composite was high, while the elastic modulus decreased substantially.     

Field-activated pressure-assisted combustion synthesis tungsten carbide–cobalt composites

FAPACS process was utilized to produce WC–10wt%Co composites from reactants’ mixtures of tungsten, cobalt and different kinds of carbon sources (activated carbon and carbon black). The Vickers microhardness of end products were 1804 kg/mm² for the former and 1899 kg/mm² for the latter.     

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.