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Abstract: The dense TiC–TiB2/Ni composite was successfully fabricated via a simple route where the pressure assisted self-propagating high-temperature synthesis (SHS) was directly ignited at 625°C with the incorporation of air. The ignition temperature in air was much lower than that in vacuum (1040°C). The composites made in air possessed the similar phase constituents and microstructure as well as comparable mechanical properties to those made in vacuum. The ignition temperature both in air and vacuum showed a significant dependence on Ni content and reactant particle size while the reaction products only showed a dependence on Ni content and B4C particle size, irrespective of Ti particle size. The density of the composite made in air and vacuum only depended on Ni content while the mechanical properties of the composites made in air and vacuum both showed a similar dependence on the Ni content and reactant particle size. [Copyright &y& Elsevier]

Abstract: The dense TiC–TiB2/Ni composite was successfully fabricated through the pressure-assisted thermal explosion reaction from Ti, B4C and Ni powder blends in air. The ignition temperature (625 °C) in air was 415 °C lower than that in vacuum. The decreased ignition temperature resulted from a chemical oven mechanism in which the oxidation and nitrification of Ti and the oxidation of B4C released the heat and promoted the occurrence of the thermal explosion reaction. The composites prepared in air and vacuum had similar phase constituents and microstructure. Moreover, the composite prepared in air possessed comparable hardness, flexural strength and fracture toughness to the composite prepared in vacuum. [Copyright &y& Elsevier]

Abstract: The fabrication of medium carbon steel–matrix composites locally reinforced with in situ TiB2–TiC particulates using self-propagating high-temperature synthesis (SHS) reaction of Ni–Ti–B4C system during casting was investigated. X–ray diffraction (XRD) results reveal that the exotherm of 1042°C initiated by heat release of the solid state reaction in the differential thermal analysis (DTA) curve is an incomplete reaction in Ni–Ti–B4C system. As-cast microstructures of the in situ processed composites reveal a relatively uniform distribution of TiB2–TiC particulates in the locally reinforced regions. Furthermore, the particulate size and micro-porosity in the locally reinforced regions are significantly decreased with the increasing of the Ni content in the preforms. For a Ni content of 30 and 40wt.%, near fully dense composites locally reinforced with in situ TiB2 and TiC particulates can be fabricated. Although most of fine TiB2 and TiC particulates which form by the reaction–precipitation mechanism during SHS reaction are present in the locally reinforced region, some large particulates which form by the nucleation–growth mechanism during solidification are entrapped inside the Fe-rich region located in the reinforcing region or inside the matrix region nearby the interface between matrix and reinforcing region. The hardness of the reinforcing region in the composite is significantly higher than that of the unreinforced medium carbon steel. Furthermore, the hardness values of the composites synthesized from 30 to 40wt.% Ni–Ti–B4C systems are higher than those of the composites synthesized from 10 to 20wt.% Ni–Ti–B4C systems. [Copyright &y& Elsevier]

Abstract: Effect of C particle size on the mechanism of self-propagation high-temperature synthesis (SHS) in the Ni–Ti–C system was investigated. Fine C particle resulted in a traditional mechanism of dissolution-precipitation while coarse C particle made the reaction be controlled by a mechanism of the diffusion of C through the TiC x layer. The whole process can be described: C atoms diffusing through the TiC x layer dissolved into the Ni–Ti liquid and TiC were formed once the liquid became supersaturated. Simultaneously, the heat generated from the TiC formation made the unstable TiC x layer break up. However, with the spread of Ti–Ni liquid, a new TiC x layer was formed again at the interface between spreading liquid and C particle. This process cannot stop until all the C particles are consumed completely. [Copyright &y& Elsevier]

Abstract: Reaction behaviors and products of thermal explosion reaction from Ni–Ti–C system under air and Ar atmosphere were investigated, respectively. The ignition temperature for the thermal explosion reaction under air is much lower than that under Ar atmosphere. Under two atmospheres, increasing the Ni content and Ti particle size can increase the ignition temperature, respectively. Under air, increasing Ni and C particle sizes can decrease the ignition temperature, but the opposite results are achieved under Ar atmosphere. The reaction products are mainly dependent on the C particle size under two atmospheres. [Copyright &y& Elsevier]

Abstract: Influence of reactant (Cr, Ti and B4C) particle size on the SHS reaction products in 30wt.% Cr–Ti–B4C system has been investigated. Particle size of Cr powder has a significant effect on the phase compositions and microstructures of SHS reaction products. The SHS reaction in Cr–Ti–B4C system with nano-size Cr goes more complete and occurs more easily than that in the system with micron-size Cr. Increase in particle size of B4C powder has a little effect on the phase compositions of SHS reaction products, which consist of TiB2, TiC and Cr phases as well as transient phase Cr5B3 and a trace of C, but results in the increase of the amount of Cr5B3. Furthermore, the average sizes of TiB2 and TiC increase from ∼0.5 and ∼1μm to ∼2 and ∼3μm, respectively, as the B4C particle size increases from ∼3.5 to 40μm. Increase in particle size of Ti powder (∼38, ∼48 and ∼74μm) has little influence on the phase compositions of the products, as well as average sizes and morphologies of TiB2 and TiC. [Copyright &y& Elsevier]

Abstract: The effect of Cr content on the self-propagating high temperature synthesis (SHS) reaction of Cr–Ti–C system has been investigated in this research. The thermodynamics calculation indicates that the TiC possesses higher thermodynamic stability than the Cr23C6, Cr7C3 and Cr3C2 phases, and the formation of TiC is the most exothermic. Additionally, the adiabatic combustion temperature (T ad) decreases with the increase of Cr content except for the phase transition regions. The XRD result shows that the type of products synthesized by SHS changes that a higher Cr content corresponds to higher chromium carbide. When Cr content is 10wt.%, only solid solution (Ti,Cr)Css is formed in the products. When Cr content increases to 20wt.%, besides (Ti,Cr)Css, the Cr7C3 phase is also detected. With the Cr content further increasing to 30 and 40wt.%, the products consist of (Ti,Cr)Css, Cr23C6, Cr7C3 and Cr, and therefore, much higher chromium carbide is synthesized. When Cr content reaches 50wt.%, however, the Cr7C3 disappears and the final products become (Ti,Cr)Css, Cr23C6 and Cr. Moreover, when Cr content increases from 10 to 20wt.%, the lattice parameter of (Ti,Cr)Css decreases, while it increases when the Cr content ranges from 20 to 50wt.%. Furthermore, the microstructure shows that the TiC particulate size decreases from ∼8 to ∼2μm with the increase of Cr content from 10 to 50wt.%, and the morphology shape of TiC particulate becomes more and more spherical. [Copyright &y& Elsevier]

Abstract: C particle size plays an important role in the ignition and combustion characteristics of the SHS reaction in the 20wt.% Ni–Ti–C system. When coarse C particles (∼38 and ∼75μm) are used, the SHS reactions consist of two different combustion stages with different brightness intensity of the combustion wave; XRD results indicate that the first and second combustion stages mainly correspond to the formation of Ni–Ti compounds and TiC ceramics, respectively. However, the final reaction is incomplete with a few Ni–Ti compounds and unreacted C. In contrast, when the fine C particle (∼1μm) is used, the SHS reaction consists of only one combustion stage with high brightness intensity of the combustion wave; XRD result indicates that final products consist of TiC and Ni, without any intermediate phase. With the decrease of C particle size, the wave velocities increase, and the ignition time becomes shorter. In addition, the morphology of TiC particulate changes to near-spherical, as C particle size decreases. [Copyright &y& Elsevier]

Abstract: The effect of Ni content on the products of Ni–Ti–B system via self-propagating high-temperature synthesis (SHS) reaction has been investigated in this research. The results show that the products of SHS reactions consist mainly of TiB2 and Ni. Besides, the transient phases of Ni4B3, Ni3B, NiB and Ni3Ti also exist in the final products, which means the SHS reactions of Ni–Ti–B system are incomplete. The change in the content of Ni within the chosen range from 30 to 70wt.% has little effect on the phase compositions of the final products. However, the sizes of TiB2 particulates have been greatly influenced by the Ni content. The average sizes of normal TiB2 particulates are nearly the same and about 4–6μm when Ni contents are 30, 40 and 50wt.%. Furthermore, TiB2 particulates in the products of these three systems present exaggerated growth and their sizes can even reach 10–15μm. The size of TiB2 particulates decreases dramatically to 1–2μm when Ni content increases to 60wt.% while to 0.6μm or less at 70wt.% Ni. The addition of Ni facilitates to form more liquid phases that are beneficial to TiB2 formation during SHS reaction process. The formation mechanism of TiB2 in Ni–Ti–B system can be characterized by the solution, reaction and precipitation processes. This can be further substantiated by the presence of remaining liquids, the typical hexagonal-prism morphology and the growth striation on (0001) crystal face of TiB2 particulates. [Copyright &y& Elsevier]

Abstract: Reaction behaviors of self-propagating high-temperature synthesis (SHS) in the Ni–Ti–B4C systems with various Ni contents were investigated. The addition of Ni supports the initiation of ignition. Theoretical calculation of the adiabatic temperatures reveals that the reactions in the Ni–Ti–B4C systems are self-sustainable for the presence of 0–66.4wt% Ni in the reactants without any preheat. The Ni content plays a significant role in controlling reaction behavior and the constituents of the final products, but can not affect the ignition process greatly. With the increase of Ni content, combustion temperatures, wave velocities and ceramic particle sizes decrease, while the ignition time shows first a remarkable decrease and then an increase with the minimum value at 20wt% Ni. [Copyright &y& Elsevier]

Abstract: The effect of Ti/C molar ratio on the SHS reaction of the Cr–Ti–C system was investigated. With the Ti/C ratio increasing, the type of products synthesized by SHS varied, and the amount of solid solution (Ti,Cr)Css increased in the final products; furthermore, also the lattice parameter of (Ti,Cr)Css increased due to the reduction in the solubility of Cr in TiC. Moreover, the combustion temperature increased, resulting in the increase of average grain size of (Ti,Cr)Css from ∼1 μm to ∼5 μm as well as the grain shape looked more and more like spherical. [Copyright &y& Elsevier]

Abstract: Four dense ceramic particulate reinforced nickel matrix composites were fabricated from Ni–Ti–C, Ni–Ti–B, Ni–Ti–B4C and Ni–Ti–C–B systems, respectively, by SHS reactions, arc melting and suction casting. The composites fabricated from Ni–Ti–C system are composed of Ni and TiC as expected, while the ones synthesized from Ni–Ti–B system are composed of Ni and Ni–Ti compounds as well as a small amount of TiB2; and the components of composites fabricated from Ni–Ti–B4C and Ni–Ti–C–B systems, respectively, are nearly the same, namely, Ni and Ni–Ti compounds as the matrices, and TiC as well as a relatively small amount of TiB2 as reinforcing particulates. Although the SHS reactions ignited by electric arc have played an important part in the synthesis of ceramic, the TiC and TiB2 particulates were formed mainly during the solidification of suction casting with the mechanism of nucleation-growth, and therefore most shapes of them are irregular. The abrasive resistance of the composites fabricated from Ni–Ti–C system is the lowest despite plenty of TiC particulates existing in the matrix; while that of the ones fabricated from Ni–Ti–B system is higher than the former though there is only a small amount of TiB2 particulates in the matrix, which is because the matrix microhardness of the latter is the highest in the four kinds of composites. However, the abrasive resistance of the composites fabricated from Ni–Ti–B system is lower than that of the ones fabricated from Ni–Ti–B4C system, which is because of the lack of sustaining and strengthening functions of ceramic particulates in the former under the condition of the small discrepancy in the two matrix microhardness; while the composites fabricated from Ni–Ti–B4C system has higher wear resistance relative to the ones fabricated from Ni–Ti–C–B system mainly due to the higher matrix microhardness of the former on the premise that the reinforcing particulates of the two composites are nearly the same. [Copyright &y& Elsevier]