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Abstract: The morphologies of primary silicon were studied in detail with different cooling rates and melt overheating temperatures. According to the present results, the morphologies of primary silicon are a strong function of the solidification conditions such as cooling rate and melt overheating temperature. With the elevation of melt overheating temperature, the morphologies of primary silicon will change from star-like and other irregular primary silicon to octahedral primary silicon and the size of primary silicon will gradually decrease. On the other hand, it can be safe to deduce that the Si–Si cluster of larger size should be beneficial for the formation of the nucleus of star-like and other irregular primary silicon and the Si–Si cluster of smaller size should be beneficial for the formation of the nuclei of octahedral primary silicon. With increasing cooling rate, the size of primary silicon will gradually decrease. If the cooling rate is lower than a certain (or critical) cooling rate, the cooling rate will have hardly effect on the morphologies of primary silicon in the solid state. If the cooling rate is higher than a certain (or critical) cooling rate, the cooling rate will play an important role in determining the morphologies of primary silicon in the solid state. [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]

Partial remelting behaviors of Mg–11Al–0.5Zn alloy and TiB2/Mg–11Al–0.5Zn composite are investigated by the isothermal holding at the temperatures of 510 and 545 °C. The result shows that, although, the TiB2 addition has no influence on the remelting characteristics of eutectic and liquidus temperatures of the composite, it has a great effect on the remaining liquid located at the grain boundary. With a processing temperature of 545 °C, the remaining liquid is dramatically decreased in the composite, compared with that in the unreinforced matrix alloy. Furthermore, the solid α-Mg grain size in the composite does not significantly reduce compared with that in the matrix alloy; however, the microhardness of the α-Mg grain is increased in the partial remelting microstructure in the composite. Although most of the TiB2 particulates are present in the remaining liquid phases distributed at the grain boundaries, some liquid islands are entrapped inside α-Mg grains. As a consequence, the TiB2 particulates can eventually reside within the grains after complete solidification. However, it is difficult that TiB2 particulate is directly incorporated (engulfed) into the Mg–11Al–0.5Zn matrix alloy during the regular solidification process. Furthermore, the DTA, SEM and XRD results reveal that no reaction occurs between the TiB2 particulate and matrix alloy during the partial remelting process, which indicates that TiB2 particulate is thermodynamically stable at the Mg–11Al–0.5Zn matrix alloy. [Copyright &y& Elsevier]

A TiB2 particulate reinforced magnesium matrix composite (MMCs) was fabricated by adding a TiB2–Al master alloy processed via self-propagating high-temperature synthesis (SHS) reaction in Al–Ti–B system into molten magnesium and using the stir casting technique. The results showed that the TiB2–Al master alloy and TiB2/Mg composite contained a certain amount of transient TiAl3 phase. When the Al–Ti–B system was incorporated with an appropriate C, TiB2 and TiC reinforcing phases were simultaneously synthesized and the TiAl3 phase was almost completely eliminated. [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: 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: Creep behavior of the unmodified and modified cast Al–Cu alloys was investigated at temperatures from 393 to 483K in the tension test. The creep resistance ability of the Al–Cu alloy modified by Pr x O y is almost 3–5 times as high as that of the unmodified Al–Cu alloy, which is attributed to a large number of nano-scale θ′ precipitates with high thermal stability in the modified Al–Cu alloy restricting and impeding the dislocation movement during the creep. The induction of a threshold stress in the analysis leads to a stress exponent of 5, which suggests that the creep behavior of both the present alloys is associated with the lattice diffusion-controlled dislocation climb (n =5). [Copyright &y& Elsevier]

Abstract: The solidification behavior of the cast TiB2 particulate reinforced AZ91 composite, including the cooling curve, microstructure and grain refinement effect, was investigated in the present study. Compared with the AZ91 alloy, the composite possessed lower nucleation temperature of primary α-Mg, almost the same eutectic reaction temperature and faster cooling rate during the total solidification time. The TiB2 particulates were pushed into the last solidified region and were surrounded by the eutectic Mg17Al12. The grain refinement effect in the TiB2/AZ91 composite can be attributed to the growth restriction effect exerted by TiB2 particulates and the faster cooling rate of the composite. [Copyright &y& Elsevier]

Abstract: An in situ AlTiSi ternary phase local reinforced aluminum MMCs composite was successfully fabricated by combustion synthesis and nonpressure infiltration course. XRD results show that the reinforced region of the composite is composed of Al and ternary AlTiSi phase with the composition closing to Ti(Al0.8Si0.2)3. The volume fraction of reinforcement can be controlled by adjusting Al content in compacts. SEM results show that the morphologies of the AlTiSi particles are polygonal and/or spherical. There exists some residual Ti surrounding by AlTiSi phase in the composites. In addition, there is some residual Si in the matrix in the form of Al–Si binary eutectic. The wettability between AlTiSi reinforcement and Al matrix is very good, and the reinforcement lies in the center of α-Al dendritic. [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: In situ TiB2 particulate locally reinforced steel matrix composites were successfully fabricated by self-propagating high-temperature synthesis (SHS) reactions in a Fe–Ti–B system containing 10, 30, 50 and 70wt.% Fe, respectively, in the molten high chromium alloy steel during casting. The locally reinforced regions of the Fe–TiB2 composites with different Fe contents in the Fe–Ti–B system consist of three different regions, i.e. the Fe-rich region, the fine TiB2 particulate region and the larger TiB2 particulate region. The portion of the Fe-rich region decreased and the larger TiB2 particulate region became unclear with the increase in Fe content in the Fe–Ti–B system. In addition, only a small amount of micropores is found in the fine TiB2 particulate region of the Fe–TiB2 composite synthesized in a 70Fe–Ti–B system, and the Fe content has obvious effect on the wear resistance of the locally reinforced region of the Fe–TiB2 composites. [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]

Abstract: A 40μm thick melt-spun ribbon was manufactured by using a single roller melt-spinning technique, and the temperature distribution of the melt-spun ribbon was obtained. The solidification time and the cooling rate of the melt-spun ribbon were estimated to be 6.59×10−5 s and 1.11×106 °C/s, respectively. The morphologies of primary silicon in the melt-spun ribbon were drastically changed to fine block-shape (maximum size of primary silicon is 5μm, minimum size of primary silicon is 0.5μm and average size of primary silicon is 2μm), and the smaller eutectic silicon can be obtained due to the rapid solidification. [Copyright &y& Elsevier]