The semi-solid deformation behavior of Ti-7Cu titanium alloy in the temperature range of 1,223 K to 1,473 K and strain rate range of 0.005 to 5 s
have been investigated by hot compressive testing. ...The results show that the maximum and stability stresses decrease with decreasing strain rate and increasing temperature. A yielding occurred to the alloy at a higher strain rate under all experimental temperatures. The flow behaviors were described by a constitutive equation based on the Arrhenius equations and the deformation activate energies is also calculated. By comparing with microstructure of the solid deformation, the liquid in semi-solid deformation can overcome the restriction of the movement of solid particle, which reduced the dislocation pile-up during deformation and caused low deformation resistant stress.
The present work is focused on the development of microstructure of Ti-7Cu alloy as a function of forging temperature and forging ratio in semi-solid state and the influence of resulting ...microstructure on the mechanical properties. The experimental results showed that the dynamic recrystallization occurred during semi-solid forging and the grain refinement was attained which is considered to be favorable for improving the semi-solid formability. The grain size increased with forging temperature and decreased with forging ratio. Forging temperature has a significant effect on the precipitation behavior in grain boundary regions during the semi-solid processing. More acicular-Ti
Cu tended to precipitate in grain boundary regions with higher forging temperature and finally formed precipitates zones adjacent to grain boundaries after forged at 1,100°C. High ultimate tensile strengths and low elongation have been achieved after semi-solid forging. The strength and hardness decreased with increase of forging temperature, while the ductility increased with increase of forging ratio. The relative contributions of tensile properties were attributed to the varieties of grain size and the distribution of Ti
Cu precipitates obtained by semi-solid forging.
Fe-based amorphous and nanocrystalline coatings were fabricated by air plasma spraying. The coatings were further treated by laser remelting process to improve their microstructure and properties. ...The corrosion resistance of the as-sprayed and laser-remelted coatings in 3.5wt% NaC1 and 1 mol/L HCI solutions was evaluated by electrochemical polarization analysis. It was found that laser-remelted coating appeared much denser than the as-sprayed coating. However, laser-remelted coating contains much more nanocrystalline grains than the as-sprayed coatings, resulting from the lower cooling rate in laser remelting process compared with plasma spraying process. Electrochemical polarization results indicated that the laser-remelted coating has great corrosion resistance than the as-sprayed coating because of its dense structure.
By introducing ceramic SiC particles, AlxCoCrFeNiTi1-x/SiC (x = 0.5,0.8 in molar ratio) high entropy alloy coatings (abbreviated as Al0.5, Al0.8, Al0.5/SiC, and Al0.8/SiC alloy coating respectively) ...were fabricated by laser cladding (LC) on the AISI1045 steel in this work. The microstructures, phase constitutions, mechanical and corrosion-resisting behaviors of the as-prepared coatings with and without SiC particles were investigated and compared intensively. It was found that the added SiC particles decomposed into the Si and C during the LC processing, which was verified to have a significant influence on constructing microstructures of the alloy coatings. The cuboidal L21 precipitates within the disordered BCC matrix in Al0.5 alloy coating transformed to the coarse lath-like microstructures composed by the L21 and FCC matrix in Al0.5/SiC. Simultaneously, the more refined braided network structures were obtained in Al0.8/SiC alloy coating, corresponding to the increased volume fraction of the B2 phase. The microhardness of the Al0.8/SiC alloy coating improved from 637 HV0.2 in Al0.8 to 718 HV0.2, and the coefficient of friction decreased from 0.40 to 0.31 with the SiC addition. In contrast, the SiC particles showed a negative effect on the microhardness of Al0.5/SiC alloy coating from 743 HV0.2 to 679 HV0.2, as a result of coarsened microstructure and increased fraction of the supple FCC solid solution. The friction coefficient reaches its lowest value of 0.29 in Al0.5 alloy coating, and there is a mixture wear mechanism of wear and delamination wear. Furthermore, the pitting potentials of both the Al0.5/SiC and Al0.8/SiC were lower than that of the SiC-free alloy coating. With the dissolution of SiC particles, the prompted spinodal decomposition and enlargement of lattice misfits between phases reduced the coatings' resistance to pitting corrosion.
•Ceramic-reinforced composites of AlXCoCrFeNiTi1-X HEA coatings without cracks were successfully prepared on the AISI1045 steel.•The added SiC particles are verified to have a significant influence on constructing microstructures of the alloy coatings.•Considerably enhanced microhardness and wear resistance were obtained in a SiC-added alloy coating, resulting from the more refined microstructure.
Annealing-induced hardening effect was studied in electro-deposited nanocrystalline Ni and NiFe thin films. Nanoindentation testing showed obvious hardening effect for all grain sizes in experiment, ...which were precisely controlled by adding Fe solutes. Contrast to the general trend in which the hardening effect monotonically increases with decreasing grain size, it enhanced firstly, peaking at a critical grain size (~ 16 nm) and then lowered. Based on the apparent inverse H-P trend and unusual enhancement of strain rate sensitivity after annealing, we attributed the weakened annealing-induced hardening phenomena, despite of the strongest grain boundary pinning effect resulted from the highest Fe solutes (up to 50 at%), mainly to the more pronounced grain-boundary mediated plasticity in extremely fine nanograins. This work contribute directly to understanding the distinct effect of alloying on mechanical properties of nanocrystalline metals.
•Unexpected weakened annealing-hardening effect of nanocrystalline NiFe alloys occurred below a critical grain size.•The apparent inverse Hall-Petch trend and the elevated m value after for annealed NiFe alloys evidenced the more pronounced GB-mediated mechanisms.•The relatively weak grain boundary pinning effect of Fe solutes, accompanied with the more pronounced grain boundary mediated activities after annealing, should be responsible for the weakened annealing-hardening effect.
In this work, Ni-Mo-SiC-TiN composite coatings were prepared by pulse electrodeposition. Through analyzing the effect of particle content on the phase structure and morphology of Ni-Mo coatings, the ...relationship between nanoparticles co-deposition amount and the mechanical properties and corrosion resistance of Ni matrix composite coatings was evaluated. The results show that the coating prepared at an electrolyte concentration of 20 g/L is flat and dense presenting the highest particle content. The crystallite size ranging from 28.27 nm to 11.85 nm is affected by different nanoparticle concentrations. As shown by the Tafel polarization and wear test, the incorporation of two hard particles improved the coating performance, and the corrosion current density was reduced by 74% to 1.84 μA/cm2. The wear rate decreased from 10.196 × 10−4 mm3/N·m to 2.65 × 10−4 mm3/N·m, and the average friction coefficient decreased to 0.11. The duplex hard particles play a bearing and hindering role during friction and corrosion. Based on the co-deposition kinetic model, a five-step pulse deposition model referring to nanoparticles was established. It is found that SiC/TiN particles co-deposited to the preferential Ni (111) crystal face and subordinate Ni (200) face. And the good binding ability between the matrix and the nanoparticles results in a high load transfer effect, thus enhancing the tribological properties of the coating. Moreover, the interaction between the duplex nanoparticles was further discussed.
The semi-solid deformation behavior of Ti14 was investigated using compression tests at deformation temperatures between 1 273 and 1 423 K with strain rate of 5×10
−2
s
−1
. Moreover, the fraction ...solid at different temperatures was also measured by image analysis. The results showed that the deformation temperature had strong effects on the flow stress, and the stress increased with the decrease of deformation temperature. The maximum stress depended greatly on the fraction solid, and a sharp decrease in stress occurred at a solid fraction between 0.94 and 0.98 (temperature from 1 323 to 1 373 K). This decrease was related to the decrease in the amount of solid bridges between grains. Because of the partial solid/liquid segregation during deformation, the experimental strain rates were much lower than those calculated by the flow of liquid incorporating solid particles, which suggested that the main deformation mechanism between 1 323 and 1 373 K was still plastic deformation of solid particles.
In this work, the effects of strain rates (10−4 s−1~10−1 s−1) on ferrite hardening of dual-phase steel were investigated through pre-straining tests. The strain localization was analyzed by the ...evolution of Kernel average misorientation (KAM). The micromechanism of ferrite hardening was elaborated by the evolution analysis of geometrically necessary dislocations (GNDs), low angle grain boundaries (LAGB) and nano-indentation. The results showed that GNDs and LAGBs in ferrite increased with increasing the strain rate, the average KAM values and nanohardness increased accordingly. Strain localization was observed in the ferrite grains at lower strain rates (10−4 s−1~10−3 s−1), and the considerable strain localization occurred at ferrite/bainite (F/B) interface at higher strain rates. Due to the nearly saturated GNDs and LAGBs density at the strain rate of 10−2 s−1, the completely ferrite hardening occurred and its nanohardness was close to dual-phase interface. During the tensile deformation after pre-straining, the yield ratio increased while the uniform elongation decreased with strain rates of pre-straining. It was worth noting that the completely ferrite hardening led to the early plastic deformation of tensile tests was interface deformation. This work provides a theoretical basis for the ferrite hardening behavior after pre-straining at different strain rates, and then contributes to the safe service of dual-phase pipeline steel.
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•At the strain rate of 10−2 s−1, due to the nearly saturated GNDs and LAGBs density, the completely ferrite hardening occurs.•After pre-straining at higher strain rates, the completely ferrite hardening leads to the early stage of plastic deformation of tensile tests is interface deformation.
WC-Co composites comparable to titanium in thermal expansion coefficient can be used as wear-resistant coatings, extending the applications of titanium alloys. This study aims to investigate the ...effect of laser power on the quality of composite coatings on the Ti-6Al-4 V substrate, and to study the phase constituents comprehensively, microstructural evolution, microhardness, and wear behavior of composite coatings. The experimental results show that there is a good metallurgical bonding between the WC-Co composite coatings with high densification and the substrate. Furthermore, a considerably high microhardness up to 1536 HV0.5, and a wear rate of 1.5 g/h were achieved owing to the synergistic effect of excellent metallurgical bonding and fine microstructures of the composite coating under laser power of 2000 W. Based on the experimental results, the process-structure-properties relationship of laser cladded WC-Co composite was established. It is expected to be applied to improve the wear resistance of petroleum titanium alloys in deep and ultra-deep wells.
•New phases W2C and η-Co were formed under the action of high energy laser density.•The morphology evolution of WC particles with different laser powers was studied.•The distribution of tensile stress eventually leads to spalling of the composite coatings.
The evolution of low angle grain boundaries (LAGBs) and Taylor factor (TF) was investigated by EBSD analysis to reveal the micromechanism of ferrite hardening for dual-phase steel during prestraining ...from 1% to 5%. The results showed plastic deformation was dominated by soft ferrite phases during prestraining from 1% to 3%, and subsequently, transformed to interface deformation during prestraining from 3% to 5%. Due to the evolution of LAGBs, dislocation substructures were generated during prestraining. The fraction of soft grains within the range of TF~2–3 gradually decreased after the hardening, indicating the slip system was more difficult to be activated within ferrite. The hardening of ferrite was attributed to the formation of stable dislocation subgrain structures and the hardening of grain orientation as well. When the prestraining degree went above 3%, the ferrite phases can be completely hardened. After ferrite hardening, the strain hardening ability of the dual-phase steel was reduced, the yield strength was increased and the uniform elongation was decreased at the same time. It was noteworthy that the stress drop (up to 10 MPa) occurred on the stress-strain curve after the completion of strain hardening, and the plastic deformation was initiated directly at interface, exhibiting a mixed mode of failure involving both cleavage brittle and dimple ductile fracture. This work is aiming to provide detailed insights and experimental evidence for ferrite hardening behaviour after prestraining, which is expected to make great contribution for better service protection of the pipeline using dual-phase steel.
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