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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 modification of in situ formed Mg2Si in Mg–Si alloys with yttrium (Y) was investigated. As-cast microstructure analysis of Mg–5wt.% Si alloys indicates that all the primary Mg2Si crystals are surrounded by a layer of α-Mg dendritic halos, which is again surrounded by the eutectic Mg2Si+Mg structures. When the Y content is 0.1 or 0.4wt.%, the sizes of primary and eutectic Mg2Si do not significantly reduce in Mg–5wt.% Si alloys. When the Y content is 0.8wt.%, the mean size of primary Mg2Si decreases from more than 100μm to about 30μm or less; furthermore, the Chinese script type Mg2Si particle also exhibits modified morphology as a fine fiber. When the Y content is further increased to 1.2wt.%, the primary Mg2Si becomes coarser again and even larger than that in the unmodified alloy; however, the eutectic Mg2Si still exhibits modified morphology as a fine size. The size and amount of Mg–Y point compounds are increased with the increasing of Y content in the alloys. In addition to distributing in α-Mg phase, the Mg–Y point compounds are also present in primary Mg2Si dendritic crystal. In the unmodified alloy, the coarse primary Mg2Si is formed by the preferred growth that occurs at the tips of branches; however, when the alloy is modified with 0.8wt.% Y, the preferred growth manner of the primary Mg2Si was depressed, while another type of growth, isotropic growth manner, is enhanced in the modified alloy. [Copyright &y& Elsevier]

Abstract: Magnesium metal matrix composites (MMCs) reinforced with 10, 20 and 30 vol.% TiB2 particulates, respectively, were fabricated by powder metallurgy. The microstructure, porosity, hardness and abrasive wear behavior of the composites were evaluated. Microstructural characterization of Mg MMCs showed generally uniform reinforcement distribution. As compared with pure Mg, the hardness (HB) values of Mg MMCs reinforced with 10, 20 and 30 vol.% TiB2 particulates were increased by 41%, 106% and 181%, respectively. The abrasive wear tests showed that the wear resistance of Mg MMCs is increased with the increasing of the reinforcement volume fraction. This was due to the strong particulate-matrix bonding and high hardness of the TiB2 particulate. [Copyright &y& Elsevier]

Abstract: Dense high volume fractions of different molar TiB2/TiC ratios reinforced Fe matrix composite were successfully fabricated through the SHS reaction assisted with pressure. The reaction mechanisms for three systems were dissolution–precipitation. The TiB2 morphology changed from plate-like to clubbed and further to cubic with decreasing TiB2/TiC ratios from 2:1 to 1:2. The composites with 2:1 and 1:1 ratios of TiB2/TiC have a similar highest Vickers hardness and flexural strength while the composite with 1:1 ratio of TiB2/TiC has the best fracture toughness. The improvement of the fracture toughness was attributed to the reduction of thermal stress and the modification of TiB2 morphology. The optimal ratio of TiB2/TiC was recommended to be 1:1. [Copyright &y& Elsevier]

The effect of Al content on the self-propagating high-temperature synthesis (SHS) reaction of the Al–Ti–C preform in molten magnesium was investigated. As the Al content in the preforms was increased over the range of 20–40 wt.%, the TiC particulate sizes decreased from ∼5.0 to ∼1.0 μm. Microstructural characterization of the TiC/Mg (AZ91D) composite showed relatively uniform distribution of TiC particulates in the matrix material and the presence of minimal micro-porosity. [Copyright &y& Elsevier]

Abstract: The microstructure, compression property and work-hardening effect of the NiAl-matrix composite reinforced by 5 vol.% ceramic particulates (TaB and TaB2) were investigated. The compression properties and work-hardening capacity (H c) under the different strain rates were also investigated. The NiAl-matrix composite has strong strain rate sensitivity. A high true ultimate strength of 1399 MPa, a true fracture strain of 18.7% and H c = 1.84 were obtained under the strain rate of 1.0 × 10−4 s−1. The good compression properties may be attributed to the refinement of the grain size and the good combination between the ceramic particulates and the NiAl-matrix. [Copyright &y& Elsevier]

Abstract: The microstructure, compression property and work-hardening effect of the NiAl-matrix composite with 1.7wt.% NbB2 and Nb x C (x =1 or 2) fabricated by the combustion synthesis and hot pressing technique have been investigated in the study. The NiAl-matrix composite has strong strain rate sensitivity. The yield strength of the NbB2–Nb x C/NiAl composite decreases while the fracture strain and the work-hardening capacity (H c) increase with decreasing strain rate. A high true ultimate strength of 1472MPa, a fracture strain of 20.1% and H c =1.41 were obtained under the strain rate of 2.0×10−5 s−1. [Copyright &y& Elsevier]

Abstract: Influence of Al addition on the products of self-propagating high-temperature synthesis (SHS) reaction in Al–Ti–Si system is investigated. When Al content is 0wt.%, the product only consists of Ti5Si3. When the Al addition is varied over the range of 5–15wt.%, the TiAl3 phase appears along with the Ti5Si3 phase. Besides Ti5Si3 and TiAl3, the transient phase Ti5Si4 is also detected in the final products when Al content increases over the range of 20–40wt.%. However, both the Ti5Si3 and Ti5Si4 phases disappear completely when Al content further increases to 50wt.%; only TiAl3 phase and trace of Al exist in the final products. Moreover, increase in Al content causes a decrease in Ti5Si3 and an increase in TiAl3 amount, which indicates that Al not only serves as a diluent but also participates in the SHS reaction process. Furthermore, the solubility of Si in TiAl3 increases significantly with Al addition increasing, while that of Al in Ti5Si3 mainly depends on the Al content in the Al–Ti–Si system. In addition, the Al incorporation has a great effect on the microstructure formation and evolution of the SHS reaction products. When Al content is less than 15wt.%, the final product mainly consists of Ti5Si3; however, which changes into Ti5(Si,Al)3 as Al content increases to 20–25wt.%, and then turns into another solid solution Ti(Al,Si)3 when Al content further increases to 30–50wt.%. Consequently, the microstructure evolution may be summarized as follows: Ti5Si3 →Ti5(Si,Al)3 →Ti(Al,Si)3. [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 effects of different processing parameters, such as heating rate, isothermal temperature and isothermal holding time, on the semisolid microstructures of the AZ91D alloy during partial remelting had been investigated in the present paper. The experimental result showed that the high heating rate shortened the growth process of renascent recrystal grains in the deformed alloys, which ultimately attributed to refine the globular α-Mg grains in the evolved semisolid microstructure. The liquid volume fraction f L of the semisolid slurry gradually enlarged with the elevating of isothermal temperature during partial remelting. The isothermal temperature between 560°C and 580°C for 30min was adequate for the AZ91D to produce an ideal semisolid slurry with liquid fraction range between 32% and 52%. During the partial remelting, it would experience a relatively long holding time that the liquid and solid phases reached a state of dynamic equilibrium in the semisolid slurry. For the AZ91D alloy, the isothermal holding time of 30min was relatively adequate for the present experiment. During the partial remelting, the primary irregular grains gradually spherodized under a function of interface curvature. Oswald ripening mechanism, a dissolution and reprecipitation diffusion-controlled growth, could account for the coarsening of globular grains in the present experiment. The spheroidization and coarsening evolution processes of solid particles in the semisolid slurry were deduced and elucidated by the corresponding simulant formulae in the present paper. [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: 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: The effects of different as-cast microstructures which were initially cast in graphite, metal, sand and firebrick moulds, respectively on the semisolid microstructure of AZ91D alloy, have been investigated during the strain-induced melt activation (SIMA) process. The experimental results showed that the moulds with high cooling capacity could produce the fine-grained as-cast microstructure in which the fine α-Mg dendrites were surrounded by a narrow layer of eutectic mixtures. After compressive deformation, in the fine-grained as-cast microstructure, the more systemic strain energy would be gradually accumulated and abundantly stored due to uniform inner crystal lattice distortion, so the recrystallization was easily induced by the stored strain energy at the elevated temperature. As a channel for the diffusion of atoms, the subgrain boundary along which Al element was enriched, foremost melted above the eutectic temperature and resulted in the separation of neighboring subgrains from primary dendrites. Therefore, the refining role of recrystallization on the microstructural evolution from dendrite to globular particles in morphology was easier to play in the fine-grained as-cast microstructure, which was advantageous for the production of fine-grained semisolid microstructure. Additionally, in the fine-grained as-cast microstructure, the melting fracture of narrow secondary dendritic arms was easy to occur in their roots, which also attributed to the production of fine globular grains in semisolid microstructure from primary dendrites. The finer dendrites in the initial as-cast alloy could evolve into the finer globular grains with relatively small grain size distribution range in the semisolid microstructure during partial remelting; therefore, the finer the dendrites in the initial as-cast microstructure, the better were the tensile properties of the evolved semisolid microstructure. [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: The effect of Al–P–Ti–TiC–Nd2O3 modifier on the microstructure and mechanical properties of hypereutectic Al–20wt.%Si alloy has been investigated. It has been concluded that Nd2O3 in Al–P–Ti–TiC–Nd2O3 modifier can modify primary silicon in hypereutectic Al–Si alloys. Statistical analysis shows that primary silicon size (approximately average 38μm) in modified Al–20wt.%Si alloy with Al–P–Ti–TiC modifier is larger than that (approximately average 20μm) in modified Al–20wt.%Si alloy with Al–P–Ti–TiC–Nd2O3 modifier. Compared with primary silicon modified with Al–P–Ti–TiC modifier, Primary silicon modified with Al–P–Ti–TiC–Nd2O3 modifier has the smaller size at different holding times such as 10, 60 and 120min. The internal defects in coarser primary silicon particles play an important role in determining the tensile strength and elongation of the materials. Coarser primary silicon particles in unmodified Al–Si alloys can degrade the loading bearing capacity of the materials. Modification can eliminate the internal defects to a great extent and improve the tensile strength and elongation of hypereutectic Al–Si alloys. Compared with unmodified and heat-treated Al–20wt.%Si alloy, the tensile strength of the modified with Al–P–Ti–TiC–Nd2O3 modifier and heat-treated Al–20wt.%Si alloy increases by 20%. [Copyright &y& Elsevier]

Abstract: The effect of predeformation on the α-Mg grains in the AZ91D alloys was investigated in different stages during the semisolid processing. The result showed that, with the increase of compressive ratio, the α-Mg dendrites in the as-cast microstructures gradually oriented themselves in the direction that was vertical to the compressive direction, and exhibited an obvious directional character. During the sequent heat treatment at 310°C for 20min, the recrystallization was induced in the deformed alloys by the increasingly accumulated systemic strain energy. The metallographical observation showed that the average size of recrystal α-Mg grains gradually reduced with the increase of compressive ratio. The reason might be that the nucleation to growth ratio of the renascent recrystal α-Mg grains gradually increased in the recrystallization process. Due to the recrystallization mechanism, the predeformation made the α-Mg grains particularly rounder and finer after the semisolid isothermal heat treatment at 560°C for 20min. The average diameter of the globular α-Mg grains in the semisolid microstructures also reduced with the increase of compressive ratio and this descending trend was almost similar to that in the recrystal microstructures, which further demonstrated that the recrystallization had an inevitable role on the evolution process of globular grains during SIMA process. While the compressive ratio surpassed 20%, the above descending trend was not so evident as that below 20%. In addition, the effect of predeformation on the tensile strength and elongation of the semisolid AZ91D alloys was also discussed in the present paper. [Copyright &y& Elsevier]

Abstract: The semisolid microstructure evolution process of the predeformed AZ91D alloy during heat treatment was studied. After being compressed by a ratio of 20.6% in height at 220°C, all the dendrites oriented in the same way. With increasing heat-treatment temperature, the dissolution of eutectic β-Mg17Al12 first took place, resulting in the primary dendritic grains coarsening into interconnected non-dendritic grains. With heating continuously, a large amount of polygon recrystallization grains occur in the microstructure. Subsequently, the residual interdendritic β-Mg17Al12 at the edges of the primary grains and the new recrystallization grains melted in succession at higher heat-treatment temperature and the primary grains separated into small polygon grains. After being heat-treated at the semisolid temperature, the amount of liquid increased until the solid–liquid system reached its equilibrium state, and the grains spheroidized. [Copyright &y& Elsevier]

The effect of predeformation on the semisolid microstructure of Mg–9Al–0.6Zn (AZ91D) alloy is investigated. The results indicate that finer, more globular semisolid microstructure was attained in more heavily deformed alloys after heat treatment at 560 °C for 20 min. Furthermore, the liquid islands in the grains also become less with the increase in the compression ratio. It is mainly because the microstructural evolution mechanisms are different in alloys with various compression ratios. The heavy predeformation leads to the occurrence of the recrystallization, and the amount of recrystallization increases with the increase of the compression ratio. These recrystallization grains can easily give rise to the small initial grains that evolve towards a globular and small morphology rapidly during isothermal heat treatment at semisolid temperature of 560 °C. Moreover, there are also no liquid islands in the final grains after evolution. In addition to the recrystallization evolution mechanism, there are two other microstructural evolution mechanisms—melting and combining of dendritic arms, which are both discussed in this paper. [Copyright &y& Elsevier]

Abstract: The pure NiAl intermetallic compound was fabricated by the combustion synthesis and hot pressing technique. Microstructure examination showed that the NiAl intermetallic compound contained fine grains. Analysis of the X-ray diffraction and the HRTEM studies showed that the phase in the intermetallics was the only NiAl phase. The NiAl showed prominent compression properties. The true ultimate compression strength and the fracture strain of the NiAl are 1002−94 +72 MPa and 21.6−1.8 +1.8%, respectively. The work-hardening capacity (H c) is 1.40−0.07 +0.09 and the Vickers micro-hardness is 360−19 +15 HV. The finer grains, the high density dislocation and the seriously distorted lattices in the matrix, and the intense interactions between dislocations contribute to the prominent compression properties. [Copyright &y& Elsevier]

Abstract: The microstructural evolution of Mg–5Si–1Al alloy during partial remelting was firstly investigated in the present study. The experimental results indicated that it was difficult to acquire the designed microstructures only by a single partial remelting, since either the globular primary Mg2Si or the granular eutectic Mg2Si phase can be produced in this process. However, the desired microstructures consisting of both globular primary and granular eutectic Mg2Si phases are successfully produced by secondary partial remelting. [Copyright &y& Elsevier]

Abstract: The Mg–30B2O3 modifier with the composition of Mg and B2O3, sintered in the temperature range between 250 and 450°C, has been developed as a low-cost and effective modifier for hypereutectic Mg–Si alloys. With 0.2–1.0wt.% B (introduced in the form of Mg–30B2O3), the morphology of the primary Mg2Si transforms from coarse dendrite shape into fine polyhedral shape with the size about 10μm. The modification mechanism of B2O3 is attributed to the adsorption and poisoning manners due to the presence of B in the melts by the decomposition of B2O3. [Copyright &y& Elsevier]

Abstract: Addition of Al can lead to the invalidation of KBF4 modification on the primary Mg2Si in Mg–5Si alloys and thus promote the preferred growth of the primary Mg2Si dendrite crystal. This may be due to the decrease or exhaustion of B in the melts by the formation of AlB x . [Copyright &y& Elsevier]