Search

Ti2AlNb‐based alloys are synthesized by spark plasma sintering from pre‐alloyed and ball‐milled Ti–22Al–25Nb powder, and the structure of the alloys is regulated by aging at 800 °C for 0.5, 1, 2, and 3 h. Comparison of phase composition, microstructure, and mechanical properties are made in this study. Aging in the B2 + O phase region refers to the reversible transformation of B2 ↔ O. Complete B2 + O Widmanstätten structure is obtained in the aged alloys synthesized from pre‐alloyed powder, and the ones from milled powder contain acicular O and B2 + O Widmanstätten structure. Ball milling eliminates the B2 + O colonies, facilitates the continuous transformation of O → B2, and induces acicular O in the alloys; however, the hardness of these alloys is decreased in contrast with that of the ones synthesized from pre‐alloyed powder. Owing to the precipitation strengthening based on a large amount of fine O‐phase precipitates, the 3 h aged alloy from pre‐alloyed powder exhibits comprehensive mechanical properties with Vickers hardness of 448 ± 9 HV, ultimate tensile strength of 730 MPa, and elongation of 0.43%. [ABSTRACT FROM AUTHOR]

The natural oxidation of amorphous Cu x Zr 1- x ( x  = 0.33, 0.5, 0.67 and 0.75) alloys has been studied by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and cross-sectional transmission electron microscopy. It is revealed that passivation behavior occurs for amorphous Cu x Zr 1- x alloys where x  ≤ 0.67, which provides an effective composition range of amorphous CuZr alloys for long time service. A thin (2–5 nm) ZrO 2 film is formed on top of amorphous alloys, with a Cu-enriched amorphous alloy layer at below. Surprisingly, tetragonal ZrO 2 nucleates between the oxide film and the alloy at room temperature in the naturally oxidized am-Cu 0.33 Zr 0.67 alloy. Amorphous Cu 2 O layer forms on top of the oxide film and surface segregation forming metallic Cu occurs for amorphous Cu x Zr 1- x when x ≥ 0.75. [ABSTRACT FROM AUTHOR]

This study aims to understand the thermal stability and annealing hardening behavior of nanocrystalline Ni(Mo) alloys at the Mo solubility limit. The microstructural and microhardness evolution of these alloys is investigated at different annealing temperatures. A rather stagnant grain growth, along with the gradual crystallization of amorphous nanostructures, in the Ni(Mo) alloys has been observed at high temperatures. The Ni(Mo) alloys with Mo content above the solubility limit exhibit an abnormal secondary hardening behavior at high temperatures, accompanied by nanosized MoNi precipitates. It demonstrates that the residual amorphous nanostructures play an important role in the thermal stability of nanocrystalline alloys. It also implies that the addition of the solute up to a solubility limit in the nanocrystalline alloys can help achieve superior strength at high temperatures. [ABSTRACT FROM AUTHOR]

• The fundamental role of atomic structure on thermal oxidation of alloys is revealed. • Al-Zr was selected as the model alloy system to circumvent preferential oxidation effect. • Structural order of parent alloys influences strikingly oxide compositions and oxidation kinetics. • Underlying mechanisms were disclosed by molecular dynamics simulations. • The study offers a new perspective in the field of surface engineering. To reveal the fundamental role of structural order of the parent alloy on the oxidation mechanism, thermal oxidation of amorphous and crystalline Al–Zr alloys with identical compositions were investigated in detail. An (Al 0.68 Zr 0.32)O 1.66 amorphous oxide emerged on crystalline Al 2 Zr, whereas an (Al 0.33 Zr 0.67)O 1.83 amorphous oxide formed on amorphous Al 68at.% Zr 32at.% under the same conditions. Oxidation kinetics was fast and linear for crystalline Al 2 Zr but slow and parabolic for amorphous Al 68at.% Zr 32at.%. The underlying mechanisms of such striking differences were disclosed by molecular dynamics simulations. The findings thus offer new prospects in the field of surface engineering. [ABSTRACT FROM AUTHOR]

Abstract Direct alloying is very difficult for immiscible alloy systems owing to the absence of driving force at equilibrium. To realize alloying for immiscible alloy systems, a method, named as irradiation damage alloying (IDA), is developed and used to prepare W/Ag, Mo/Ag and Mo/Cu laminated metal composites (LMCs) in this work. The IDA process mainly includes three steps: firstly, the multi-energy Ag (or Cu) ions were implanted into the surface of the W (or Mo) matrix; secondly, an Ag (or Cu) coating layer was deposited on the damaged W (or Mo) matrix by vacuum evaporation; thirdly, the obtained W/Ag (Mo/Ag or Mo/Cu) laminated bimetallic samples were annealed at 950 °C in hydrogen for 8 h. It is confirmed that diffusion alloying of immiscible metal atoms indeed takes place and metallurgical bonding interfaces have been constructed successfully. Additionally, to reveal the underlying mechanism of IDA, a thermodynamic model is introduced. It is shown that the storage energy caused by irradiation damage in the matrix metal and the surface energy of the coating layer dominate the thermodynamic driving force. Besides, the storage energy has been confirmed to play a decisive role for the microstructure development of the metallurgical bonding interface. Graphical abstract Unlabelled Image Highlights • The newly developed IDA is a feasible way to realize direct alloying for immiscible systems. • W/Ag, Mo/Ag and Mo/Cu metallurgical bonding interfaces have been constructed successfully by means of IDA. • The storage energy caused by irradiation damage and surface energy of coating layer dominate thermodynamic driving force. • The decisive role for the microstructure development is the storage energy caused by irradiation damage. [ABSTRACT FROM AUTHOR]