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In this paper, the high strength and lightweight Al–Cu–Li alloy (AA2099) is considered in as-built and preheated conditions (440 °C, 460 °C, 480 °C, 500 °C, and 520 °C). The purpose of this study is to investigate the influence of laser powder bed fusion (LPBF) in situ preheating on precipitation microstructure, mechanical and corrosive properties of LPBF-printed AA2099 alloy compared to the conventionally processed and heat-treated (T83) alloy. It is shown that precipitations evolve with increasing preheating temperatures from predominantly globular Cu-rich phases at lower temperatures (as-built, 440 °C) to more plate and rod-like precipitates (460 °C, 480 °C, 500 °C and 520 °C). Attendant increase with increasing preheating temperatures are the amount of low melting Cu-rich phases and precipitation-free zones (PFZ). Hardness of preheated LPBF samples peaks at 480 °C (93.6 HV0.1), and declines afterwards, although inferior to the T83 alloy (168.6 HV0.1). Preheated sample (500 °C) shows superior elongation (14.1%) compared to the T83 (11.3%) but falls short in tensile and yield strength properties. Potentiodynamic polarization results also show that increasing preheating temperature increases the corrosion current density (Icorr) and corrosion rate. Indicated by the lower oxide resistance (Rox), the Cu-rich phases compromise the integrity of the oxide layer. [ABSTRACT FROM AUTHOR]

During the service process of the mechanized fishing boat, its low carbon steel hull and parts are extremely susceptible to Cl− erosion and seawater scouring, which cause a decrease in strength and lead to failure. To increase its service life and reduce maintenance costs, coating protection technology is widely used. In order to solve the problem of poor adhesion between paint coating and substrate and low strength of metal coating, NiCrMo-WC coatings with different WC contents (0 wt.%, 5 wt.%, 10 wt.%, 15 wt.%, 20 wt.%) were prepared on the surface of Q235 substrate by plasma cladding technology. The coatings were characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), energy spectrum analysis (EDS), etc. Its phase formation rule, microstructure and element distribution were studied. Microhardness test and electrochemical corrosion test were carried out. The study found that the 20 WC coating has the highest average hardness (563.1 HV). It is about 3.25 times of the Q235 substrate. It has the lowest friction, wear rate and lower friction coefficient, showing the best wear resistance. The 15 WC coating has the lowest self-corrosion current density (3.4934 × 10−7 A/cm2) and the lowest corrosion rate (0.0041 mm/a), which is only 3.7% of the corrosion rate of Q235 steel. [ABSTRACT FROM AUTHOR]

In the present work, isothermal lower bainitic transformation with nano‐sized cementite (θ) precipitation is simulated by means of multiphase‐field approach. In order to simulate the very fine cementite, ultra‐small grid spacing, that is, 2 nm, is applied. A faceted anisotropy model is coupled in the simulation of both bainitic ferrite (αB) and cementite (θ) growth. The simulated microstructure evolution and bainite fraction are compared with experimental results. Carbon redistribution across γ/αB and αB/θ phase boundaries during lower bainitic transformation is further discussed. [ABSTRACT FROM AUTHOR]

The formation of nanoscale precipitates influences the uniform mechanical properties of steels. The precipitation behavior in a Ti‐bearing steel with 50% hot deformation is investigated at different continuous cooling rates, including 0.5, 2, and 5 °C s−1. It is found that both the random precipitation and the interphase precipitation are observed in the hot deformed steel by means of transmission electron microscopy (TEM). At the cooling rate of 0.5 and 2 °C s−1, the interphase precipitation and the random precipitation occur even in the same ferrite grain. When the cooling rate is 5 °C s−1, the interphase precipitation disappears and only the random precipitates exist in the small ferrite grains. The morphologies of the interphase precipitation change from the irregular curved type (I‐CIP) to regular curved type (R‐CIP), and finally to the regular planar type (PIP) with the increase of the cooling rate. The interphase precipitation adjacent to the ferrite grain boundaries reveals its preferential occurrence in the final stage of the transformation. Compared with the isothermal heat treatment, the control of precipitation behavior via cooling rate adjustment is easier and less time‐consuming to obtain tailored mechanical properties of the steel. [ABSTRACT FROM AUTHOR]

Medium-Mn steels are characterized by ultrafine-grained (UFG) duplex microstructure consisting of ferrite and a large amount of retained austenite. Intercritical annealing is of great importance to achieving the UFG duplex microstructure and adjusting amount as well as stability of retained austenite. In the present work, the influence of intercritical annealing temperature on the microstructure and mechanical properties was investigated in a cold-rolled medium-Mn steel Fe-12Mn-3Al-0.05C. Particularly, the dependence of microstructural morphology on intercritical annealing temperature was emphasized to reveal the genesis of the microstructural morphology in medium-Mn steels. The ferrite-austenite duplex microstructure manifested an elongated morphology in the specimen annealed at 555 °C, which inherited the lath structure of the cold-rolled state. The medium-Mn steel exhibited a continuous yielding behavior and a relatively low strain-hardening rate. With an increase in intercritical annealing temperature up to 650 °C, the amount of retained austenite increased and microstructure was partially recrystallized, showing a mixture of elongated and equiaxed grain morphologies. When the intercritical annealing was applied at 700 °C, the medium-Mn steel mainly exhibited recrystallized microstructure with equiaxed morphology. The optimal balance between the amount and the stability of retained austenite led to an enhancement of strain hardening and ductility. With a further increase in the intercritical annealing temperature to 750 °C, the medium-Mn steel possessed pronounced strain-hardening behavior at the beginning of the tensile deformation with deteriorated ductility. [ABSTRACT FROM AUTHOR]

In this work, we prepared titanium matrix composites (TMCs) reinforced with in-situ polycarbosilane (PCS)-derived TiC particles. The effects of PCS addition on the microstructure, interface, hardness, and tribological properties were studied. The pyrolysis of PCS leads to the formation of in-situ TiC particles and Si solid-solution at a low PCS content (≤3 wt%). The TiC particles with a particle size of 4.8 μm are uniformly distributed in TMCs and have a well-bonded interface with the Ti matrix. The average grain size of α-Ti decreases from 100.5 μm in pure Ti to 16.1 μm in the Ti-3 wt% PCS composite. The presence of in situ synthesized TiC particles contributes to the excellent wear resistance of the Ti/PCS composites, which is ascribed to the increased hardness, superior load transfer capability, and oxidation wear resistance. The Ti-3 wt% PCS composite possesses the hardness of 4.72 GPa, elastic modulus of 169.23 GPa, and a low specific wear rate of 0.84 × 10−12 m3/(N·m) under constant conditions (3 N, 0.03 m/s). These values are all superior to those of Ti-6Al-4V alloy. This work sheds light on the design of high wear-resistant TMCs for industrial applications. • The in-situ PCS-derived TiC reinforced Ti matrix composites were fabricated. • The in situ synthesized TiC particles had a strong interface with Ti matrix. • The Ti/PCS composite obtained the excellent wear resistance. [ABSTRACT FROM AUTHOR]