•Molten Ni1−xAlx is dominated by pentagonal bipyramids.•Strong affinity between Ni and Al induces significant chemical order.•Al atoms try to avoid bonding to Al so as to form Ni–Al bonds as many as possible.•The chemical order is enhanced with increasing Al concentration.The local structures of molten Ni1−xAlx (x = 0.102, 0.148, 0.204 and 0.25) at 1773 K have been studied by ab initio molecular dynamics simulations. Molten Ni1−xAlx is dominated by pentagonal bipyramids, while just small amounts of full icosahedral short-range orders (ISROs) are found. Most of the geometrical short-range orders (SROs) are more complex than a full ISRO. Generally, BCC-, FCC- and HCP-SROs do not exist in molten Ni1−xAlx. Strong affinity between Ni and Al induces significant chemical order. Al atoms try to avoid bonding to each other and prefer dispersing in the melt so as to form Ni–Al bonds as many as possible. Distorted zinc-blende-structure like network composed by Ni–Al bonds is formed gradually due to the strong affinity between Ni and Al and the growing Al concentration. With increasing Al concentration in molten Ni1−xAlx, the chemical order is enhanced and the geometrical order is weakened accordingly. The strong affinity between Ni and Al also induces the shell around Al being densely packed, which hinders the diffusion of Al.

•Short range orders in molten Al have been studied using AIMD simulations.•A set of indices (l2,l3,l4…lj) have been defined to differentiate the SROs.•FCC- and HCP-SROs do not exist in equilibrium molten Al generally.•Some specific SROs induce that the self-diffusion constants obey different Arrhenius relationships in temperature ranges lower and higher than 1073 K.Short range orders (SROs) in molten Al from 943 to 1523 K have been studied through ab initio molecular dynamics simulations. Pair-correlation functions, bond-angle distribution functions, Honeycutt and Andersen analysis were employed to study the local structure of molten Al. A set of indices (l2,l3,l4…lj) were defined to differentiate the SROs. FCC- and HCP-SROs do not exist in equilibrium molten Al generally. Small amount of icosahedral or icosahedron-like SROs are found in molten Al and the structures of the most SROs are more complex than an icosahedron. The non-monotonous or non-classical evolution for the amount of the specific SROs, with five and six 15xx + 1431 (sum of 15xx and 1431) bonded-pairs packing around the central atom, induce that the evolution of self-diffusion constants obeys different Arrhenius relationships in temperature ranges lower and higher than 1073 K.Graphical abstract

The formation energies of various point defects in Al3Ti(D022) have been calculated by using first-principles calculation. The effects of vacancies on Si site preference were examined to better understand Si substitution behavior in Al3Ti. The results show that, under Al-rich condition, the formation energy of antisite AlTi is the lowest than those of other point defects, and Ti vacancy is more preferred than Al vacancy. But Si prefers to occupy Al vacancy compared with Ti vacancy which causes a finite solubility of Si in Al3Ti system. The calculation is instructive for the further improvements of process of Si removal.Highlights► For antisites in Al3Ti, formation energy of AlTi is lowest under Al-rich condition. ► The most probable vacancy in Al3Ti is Ti vacancy under Al-rich condition. ► Al vacancy formation is more preferred than Ti vacancy formation under Ti-rich condition. ► Al vacancy is helpful to Si doping in Al3Ti.

The low-index surfaces of TiN are calculated using the first-principles method based on density functional theory. It is found that the relaxation effect is mainly localized in the outmost three layers for all surfaces, and the distance reduction of the outmost interlayer for the N-terminated (111) surface is much larger than other surfaces. The N-terminated (111) surface is thermodynamically favorable at high nitrogen chemical potential, which is consistent with the experimental results.

A deliberately prepared Fe-Ti-N master alloy was employed as a grain refiner for the 409L ferritic stainless steel in an attempt to refine the as-cast solidification structure. It was found that the average equiaxed grain size of the sample deceased from 1503 to 303 μm and the proportion of equiaxed grain zone increased from 14 to 100 pct with increasing the Fe-Ti-N master alloy addition level to 2.5 wt pct. Hence, this method may have good prospects for industrial applications.

A TiN-matrix coating with a thickness of about 400 μm was prepared by reactive high velocity oxygen fuel (HVOF) spraying on carbon steel in air. The phase composition, microhardness, and antiabrasion properties of the coating were investigated using x-ray diffraction (XRD), an energy dispersive spectrometer (EDS), a scanning electron microscope (SEM), a Vickers microhardness tester, and block-on-ring abrasive equipment. The abrasion mechanism of TiN-matrix coating under dry abrasion conditions was also discussed. The results indicate that the composition of the coating is main phases of TiN and TiN0.3, minor phases of Ti2O3, and TiO2. The TiN-matrix coating possesses high microhardness and relatively good toughness. Furthermore, the friction coefficient of the coating decreases with the increment of applied load. The interstratified distribution of titanium oxides can act as a solid lubricant during the wear test. The main abrasion mechanism of the TiN-matrix coating is adhesion wear. In addition, the coating with self-lubricating property can improve the antiwear property of the substrate significantly.

TiN-matrix coating was prepared by reactive high velocity oxygen fuel (HVOF) spraying on carbon steel based on the self-propagating high temperature synthesis (SHS) technique in air. The phase composition, structures, and properties of TiN-matrix coating were analyzed using XRD, EDS, SEM and Vickers microhardness equipment. The anti-corrosion property in nearly neutral 3.5 wt% NaCl electrolytic solution was measured. The Weibull distribution of Vickers microhardness at different loads and their linear fitting were analyzed. The apparent fracture toughness of the coating was also calculated. The coating is composed of main phases (TiN, TiN0.3), minor phases (Ti2O3, TiO2), and porosity. The anti-corrosion property of an HVOF-sprayed TiN-matrix coating in electrolytic solution is superior to that of AISI 316L stainless steel. The microhardness values from 1137HV0.05 to 825HV1 are relatively high and have indentation size effect (ISE). With the increment of m, which increases with the increment of applied load, the microhardness values are more concentrated. The average value of apparent fracture toughness KIC is \( 4.62\,\hbox{MPa} \cdot m^{{\frac{1} {2}}} \). It is higher than that of reactive plasma sprayed (RPS) TiN coating, which reflects the good toughness of a TiN-matrix coating deposited by reactive HVOF spraying.

The cracking failure of a conventional thermal barrier coating (TBC), consisting of a near-α titanium substrate, a NiCoCrAlY bond coat (BC), and a 8 wt.% yttria-stabilized zirconia ceramic layer deposited by electron beam-physical vapor deposition (EB-PVD) method, was studied by cyclic furnace testing and isothermal exposure. The scanning electron microscope, electron probe microanalysis, and microhardness indentation were used to probe the failure mechanism. It is found that due to the mismatch of the coefficient of thermal expansion, the as-deposited BC is suffered the long-term tensile creeping at room temperature. During the high-temperature exposure, the TBC locally rumples, bringing in-plane tensile stress at the shoulders, and out-of-plane tensile stress at the peak of the rumpled BC, where primal cracks are originated. During the cooling period, the ridges of substrate pulled by the local rumpling of the BC blocks the contracting of the BC, originating new cracks in planar BC, and aggravating the original cracks. Furthermore, the oxidation products pushed into the BC and the 8YSZ enlarges the TBC and cracks the substrate along the weakest diffused grain boundaries. The cracking failure related to the diffusion of the BC to the substrate is also discussed.

High quality Tm-doped YAlO3 (Tm:YAlO3) single crystals were obtained along crystallographic b-axis by the Czochralski technique. Optical absorption and fluorescence spectra for Tm3+ in YAlO3 crystals were investigated at room temperature. Based on Judd–Ofelt approach, the intensity parameters Ωt (t = 2, 4, 6) of Tm:YAlO3 were calculated to be Ω2 = 0.93 × 10−20  cm2, Ω4 = 2.23 × 10−20 cm2, and Ω6 = 1.12 × 10−20 cm2. The spectral parameters such as experimental and theoretical oscillator strengths, radiative transition probabilities, radiative lifetime and the fluorescence branching ratio were also obtained. All results indicate that Tm:YAlO3 is a potential candidate for compact, efficient mid-infrared lasers with laser diode pumping.

Two kinds of thermal barrier coatings (TBCs), consisting of NiCoCrAlY bond coats (BCs) deposited by electron beam-physical vapor deposition (EB-PVD) and high velocity oxy-fuel (HVOF) thermal spraying, respectively, and top 8 wt%Y2O3–ZrO2 (8YSZ) ceramic layers deposited by EB-PVD were prepared on near-α titanium alloys. The field emission scanning electronic microscopy and microhardness indentation are used to study the microstructure and microhardness. Different failure features including cracking patterns and the delamination degree of these two TBCs are discussed according to the thermal cycling tests in the atmosphere. It is found that the morphology of the two BCs deposited by different methods (EB-PVD and HVOF) determines the microstructure and microhardness of their corresponding top 8YSZ layers. The BC prepared by EB-PVD is dense and homogeneous, which leads to a dense and hard 8YSZ with clustered slim columnar grains. The BC prepared by HVOF, however, is porous and inhomogeneous in microstructure and, as a result, the top ceramic layer is loose with low microhardness and clustered coarse columnar grains.

Three Cu–Fe–Ag in situ composites, i.e. Cu–14 wt.%Fe–1 wt.%Ag, Cu–14 wt.%Fe–3 wt.%Ag and Cu–11 wt.%Fe–6 wt.%Ag were prepared by cast and drawn process. Microstructure evolution and mechanical properties of the composites were investigated. The results show that the presence of Ag can strengthen the composite and the fracture surfaces of Cu–Fe–Ag composites exhibit shear characteristics at lower draw ratio. The ultimate strength of the above three Cu–Fe–Ag composites reached 1119 MPa, 1578 MPa and 1357 MPa in sequence at draw ratio η = 6.1, however that of the same processed Cu–12 wt.%Fe is only 978 MPa. The higher strength of Cu–Fe–Ag results from the strengthening effect of Ag: (1) refining the primary Fe dendrites and reducing the spacing between the filaments; (2) solution and precipitation strengthening the copper matrix and (3) strengthening the composite in the form of aligned Ag filaments if the amount Ag is enough for the formation of Cu–Ag eutectic under certain solidification conditions.

Aging characteristics of Cu–12Fe and Cu–11Fe–6Ag in situ composites were investigated. Curves of Vickers hardness vs. temperature, and electrical conductivity vs. temperature for the aged composites were plotted. Cu–11Fe–6Ag exhibits special hardness and conductivity peaks at about 350 °C. Microstructure investigations by scanning electron microscopy and transmission electron microscopy reveal that the presence of Ag can harden the composite at temperatures lower than 350 °C and accelerate the precipitation kinetics of Fe in the copper matrix.

Deoxidation of both cathode and recycled copper by calcined charcoal filtration was conducted experimentally. The oxygen concentrations as well as the electrical resistivities of samples were measured. Results show that charcoal filtration is very suitable for manufacturing oxygen free copper. It is an effective method for oxygen removal from molten copper, and does little harm to the electrical conductivity of copper. With proper filtration process, the oxygen concentration in the recycled copper melts can be controlled under 5 ppm or less, and the electrical resistivity of the filtered sample is about 1.750 μΩ cm.

The low-index surfaces of TiN are calculated using the first-principles method based on density functional theory. It is found that the relaxation effect is mainly localized in the outmost three layers for all surfaces, and the distance reduction of the outmost interlayer for the N-terminated (111) surface is much larger than other surfaces. The N-terminated (111) surface is thermodynamically favorable at high nitrogen chemical potential, which is consistent with the experimental results.