Local supersaturation during melting in a temperature gradient

A homogeneous single-phase Al–Cu alloy was exposed to a steep temperature gradient for a short time interval, melting of the sample at the hot end was interrupted at intermediate stages. In the resolidified microstructure, the local supersaturation was determined by analysing concentration profiles across former liquid films at grain boundaries and adjacent zones in the grain interior. Already at moderate heating rates (3 K/s) significant supersaturations occurred and were quantified.     

Friction and wear behaviour of Inconel 718 alloy fabricated by selective laser melting after heat treatments

ABSTRACT

The effect of heat treatments (solution and double aging) on friction and wear behaviour of Inconel 718 (IN718) alloy fabricated by selective laser melting (SLM) were studied. After heat treatment of solution and double aging, the friction and wear of the alloy have been improved. The worn surfaces of heat-treated IN718 alloy became smoother, and micro-ploughing became shallower. After solid solution hearting, a portion of the Laves phase ((Ni, Fe, Co)₂(Nb, Ti, Mo)) dissolves into the matrix, after which the γ″ phase (Ni₃Nb) andthe equilibrium phase of the δ phase (Ni₃Nb) precipitates during double ageing. After solution and double aging, nano-scale γ′ (Ni₃(Al, Ti)) and γ″ phases distribute homogeneously in the matrix, which improves the material hardness and wear resistance of the SLMed IN718 alloy.     

On the synthesis and characterisation of novel composite-structured high-entropy alloys

A study of novel composite-structured CoCrFeNi₃Si, CoCrFe₂Ni₂Si and Co₂CrFeNi₂Si high-entropy alloys, synthesised by vacuum arc melting, is presented. The designing criteria for the formation of such alloys were based on the enthalpy of mixing and the valence electron concentration. X-ray diffraction analysis revealed that all the alloys were composed of face-centered cubic and intermetallic phases. Scanning electron microscopy, along with elemental analysis, indicated that the face-centered cubic phase mainly contains Co, Cr, Fe and Ni, whereas, the intermetallic compound is Ni-Si rich. All the synthesised high-entropy alloys in the present investigation possess excellent compressive strength along with ductility at room temperature, suggesting significant potential application in the engineering field. Furthermore, enhanced hardness, wear resistance and corrosion resistance were achieved in all the designed high-entropy alloys. The previously given design parameters for the composite-structured high-entropy alloys are in good accord with the current research work.     

Transcending Lindemann's predictions for the melting temperatures of metals and for the long-wavelength limit of their liquid structure factors

Lindemann's melting criterion remains useful. However, one prediction it makes for liquid metals (our focus here) is that the long-wavelength limit of the structure factor S(q) at freezing, S _{T m} (0), where T _m is the melting temperature, is a universal constant. For 34 metals we have calculated S _{T m} (0) from input data, which is essentially the measured T _m and the surface thickness L, defined near freezing as the product of isothermal compressibility and surface tension. To complete the characterization of S _{T m} (0) we fit to one metal, chosen as Rb, for which S _{T m} (0) is well established experimentally. For a wide variety of metals considered, S _{T m} (0) is then found to vary by a factor of 10.     

理雅各宗教思想中的中西融合倾向

伦敦会传教士、汉学家理雅各(1815-1897)受其家乡苏格兰的神学思想和非国教家庭背景的影响而产生了独立、开放的宗教意识。尽管他以自身的信仰为本位,但在对中国文化的诠释和评价上表现出了明显的中西宗教融合的倾向,这使他在西方传教士中处于颇为孤立的境地。     

Melting point depression method for determining the solid–liquid interfacial energy of metal elements: theoretical validation and updated compilation of data

Comparative analyses of the crystal nucleation method and the melting point depression (MPD) method for measuring the solid–liquid interface energy γ_sl are carried out. The MPD method is found more reliable and has several advantages from experiment through data analysis to theoretical generalisation. The MPD data in use, all reported before the 1970s, are updated with the derived γ_sl re-compiled. Finally, by invoking a melting model that we developed recently, an equation for calculating γ_sl is proposed on basis of the melting point depression method.     

Investigations of the optical spectra and local structure for nickel(II) ions in XF2 (X = Mg,Zn) single crystals

A complete diagonalization energy matrix method (CDM) is proposed for 3d ⁸ ions in orthorhombic site (D _{2 h} ) symmetry. As an application, the optical spectra of XF₂ : Ni²⁺ (X = Mg, Zn) is well explained on the basis of both the CDM and the semi-self-consistent field d-orbital (semi-SCF d-orbital) theory. In addition, by establishing the relationship between the optical spectra and local structure, it has been possible to calculate the crystal structure parameters for XF₂:Ni²⁺ from optical measurements on Ni²⁺ ions. The theoretical results are in good agreement with experimental findings.     

Mechanochemical synthesis for studying the melting of metallic nanoparticles: a case study of copper

Mechanochemical synthesis is a promising method for studying the size-dependent melting of metals if the size of the resulting metallic nanoparticles can be tuned effectively. Here, with Cu as an example, we show that tuning of particle sizes can be accomplished by extending the milling time at a high milling speed and following annealing of the milled samples. With the so prepared samples, the melting point depression of Cu nanoparticles and its size dependence are successfully investigated.