Band 112, Heft 11

In this study, 2D TiC nanosheets were successfully synthesized by reacting carbon black and Ti 2 AlC in a molten NaCl/KCl eutectic salt. The effects of salt content and ratio of raw materials on the phase composition and purity of TiC products were systematically investigated. Results showed that carbon black enhanced the total decomposition of Ti 2 AlC to TiC, Al, and Al 3 Ti at 1100 °C. The introduction of molten salt ensured the formation of TiC nanosheets. Excess carbon influenced the synthesis of high TiC content by removing the Al and Al 3 Ti by-products. TiC nanosheets had a thickness of approximately 10–20 nm and a length of approximately 150–200 nm. A possible synthesis mechanism of TiC nanosheets was proposed.

The crystallisation kinetics of (Cu 46 Zr 46 Al 8 ) 100–x Gd x ( x = 0, 2 and 4 at.%) bulk metallic glasses in non-isothermal and isothermal conditions were studied by differential scanning calorimetry and X-ray diffraction. X-ray diffraction analysis shows that the crystallisation product Cu 10 Zr 7 changes to Cu 10 Zr 7 and Cu 2 Gd in the presence of Gd in non-isothermal and isothermal conditions. Crystallisation activation energy was calculated using the Kissinger and Ozawa methods in non-isothermal conditions and using the Arrhenius model in isothermal conditions. The results show that Gd addition triggers an increase in the energy barrier during crystallisation. The Johnson–Mehl–Avrami model was employed to analyse the crystallisation kinetics in the isothermal condition. The Avrami exponent, n , for Cu 46 Zr 46 Al 8 is more than 2.5, which demonstrates that the crystallisation is mainly governed by diffusion-controlled three-dimensional growth with increasing nucleation rate. Comparably, n for (Cu 46 Zr 46 Al 8 ) 98 Gd 2 and (Cu 46 Zr 46 Al 8 ) 96 Gd 4 is 1.5 < n < 2.5, which suggests that the crystallisation is mainly determined by diffusion-controlled three-dimensional growth with decreasing nucleation rate.

(Mn,Fe) 2 (P,Si)-basedmaterials are promisingly applied in the room-temperature magnetic refrigeration field. In this study, Mn 1.25 Fe 0.7 P 0.5 Si 0.5 Cx ( x = 0, 0.01, 0.03 and 0.05) alloys were prepared by arc-melting and then a two-stage sintering process. The effects of C doping on the crystal structure and magnetocaloric behavior are discussed. Results indicate that the Fe 2 P-type structure (space group of P62 m) was crystallized for all samples with weakened first-order magnetic transitions (FOMT). The Curie temperature could be altered from 223.5 K to 278.5 K with the large magnetocaloric effect (MCE) remaining by C doping. In the applied magnetic field of 5 T, the peak value of magnetic entropy change (–Δ S M ) increased by 7.3% to reach 25.1 J × kg –1 × K –1 . The temperature-induced entropy change (Δ S DSC ) derived from DSC was slightly larger than Δ S M induced by the magnetic field. The Mn 1.25 Fe 0.7 P 0.5 Si 0.5 alloys with large MCE can be effectively tuned by C doping because C atoms prefered to share the substitute and occupy the interstitial sites in hexagonal Fe 2 P-type structure.

The composition design of complex concentrated alloys originates from the composition design of amorphous alloys. To expand the composition design of alloys, herein, the compositions of novel Ti–Co–Ni–Zr complex concentrated alloys were obtained by the proportional mixing of Ti 2 Co intermetallics and Ni 64 Zr 36 binary eutectic. The theory and method of this new alloy design are also discussed. The as-cast Ti 28 Co 14 Ni 37.12 Zr 20.88 , Ti 30 Co 15 Ni 35.2 Zr 19.8 , and Ti 32 . Co 16 Ni 33.3 Zr 18.7 alloys were composed of body-centered cubic TiNi and Ti 2 Ni phases. The Ti 28 Co 14 Ni 37.12 Zr 20.88 alloy exhibited high yield strength (2 164 MPa) and compressive strength (2 539 MPa) under quasi-static compression at roomtemperature. The high strength of Ti 28 Co 14 Ni 37.12 Zr 20.88 alloy is related to the precipitation of Ti 2 Ni along the grain boundary and the precipitation in the crystal. This paper validates that using the proportional mixing method of intermetallics and eutectic alloy is an effective method to design complex concentrated alloys with high strength.

This study presents the modification effect of trace vanadium on the in-situ formed TiB 2 particles in as-cast aluminum composites. With 0.2 wt.% V addition the morphology of TiB 2 was modified from hexagonal platelet or irregular feather-like shape to hexagonal prism or rectangular prism with parallel growth steps along the c -axis. Meanwhile, V rich cores were detected in the center of TiB 2 and the exposure of the high-index crystal plane (1101) TiB2 was detected in Al-0.2 wt.%V. Statistical analysis of the particle size and aspect distribution both in commercial Al and Al-0.2 wt.%V was conducted. The elemental distribution and scanning electron microscopy investigation revealed that VB 2 may serve as the 2D-nucleus of TiB 2 particles. The growth mechanism of TiB 2 under the influence of V was explored.

Friction stir processing was used to prepare aluminium metal matrix composite reinforced with B 4 C particles. The micro-hardness of the composite was improved by selecting the process parameters. Friction stir processing parameters, namely tool rotational speed, tool tilt angle and different pin profiles, were explored by using Taguchi’s L9 orthogonal array and analysis of variance. Optical microscopy and scanning electron microscopy were employed for microstructural analysis. X-ray diffraction was used to evaluate the residual stress. Experimental results illustrated that increased rotational speed, reduced tilt angle and square pin profile of the tool gave more uniform dispersal of B 4 C content with maximum micro-hardness. Small amounts of compressive residual stress developed at the stirred and thermo-mechanically affected zones confirmed the adequate improvement in micro-hardness. Micro-hardness of fabricated Al 6063/B 4 C composite surfaces was enhanced by 30% as compared to Al 6063 alloy.

Surface mechanical nano-alloying treatment (SMNAT) was employed to fabricate a nanostructured Ti coating on LZ91 Mg–Li alloy. Microstructure, surface hardness and in-vitro biocompatibility of the Ti-coated sample were investigated in comparison with those of an untreated sample. Experimental results showed that a nanostructured Ti coating with a thickness of 35 to 60 μm was formed after SMNAT for 2 h. The average grain size in the top surface of the Ti coating was about 30 nm. The surface of the Ti coating is rougher than that of the untreated LZ91 sample, in which the values of Ra , Rq and Rz were 7.83, 9.57 and 14.85 μm, respectively. The hardness of the Ti coating top surface was about 483 HV. Cell proliferation and differentiation on Ti coated samples were enhanced relative to those on the untreated samples.

In this paper, pure cubic chromium silicide (Cr 3 Si) hollow particles have been successfully synthesized through the solid-state reaction of chromium sesquioxide, silicon powder and metallic lithium in an autoclave at 600 °C for 10 h. The as-prepared samples were characterized by means of X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy, which showed that the as-prepared samples were cubic phase Cr 3 Si hollow particles. Furthermore, the oxidation resistance of the obtained Cr 3 Si sample was also investigated.

Hydroxyapatite with the chemical formula Ca 10 (-PO 4 ) 6 (OH) 2 is an important bioceramic well known for its high osteoconductive properties, non-toxic nature, high bioactivity and good biocompatibility. Moreover, it is known to mimic natural bone. Inspite of the above mentioned advantages, it has certain disadvantages such as having poor mechanical properties, being brittle, not showing an inhibitory effect on microbes and taking a long time to resorb in the body. These disadvantages can be covered up by the addition of dopants which include cations, anions and polymers. These are sufficiently known to improve the properties of hydroxyapatite. This review focuses on the substitution of hydroxyapatite with silver, zinc, magnesium ions and alloys to show the changes in the morphology and biocompatible properties of hydroxyapatite after substitution of the ions in the matrix.