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[en] In this study, the mechanical properties and corrosion resistance of LA143 alloy specimens produced by severe plastic deformation (SPD) were investigated. It was found that SPD was an effective way to simultaneously improve the Vickers hardness and corrosion resistance of LA143 alloy specimens in 3.5 mass% NaCl aqueous solution.
[en] The disappearing and forming behavior of B2 ordered phase in high Si steels with Si-levels between 5 and 6.5% (by weight, unless specified otherwise) was investigated by observing TEM and measuring electrical resistivity and micro- and nano-hardness. The critical cooling rate for suppressing the formation of B2 ordered phase increased exponentially with Si-content. The ordered phase coarsening was observed to occur actively above 800 deg. C, where atoms have enough mobility. The removal of solidification segregation is necessary in order to reduce the amount of B2 ordered phase in the as-cast or hot-rolled state, to lower the annealing temperature for the dissolution of B2 ordered phase, and to shorten the annealing time. Micro-Vickers hardness depended only on Si-content even under various heat treatment conditions, and the nano-hardness had a small difference between B2 and A2 phases. In the high Si steels, the short-range order in A2 disordered phase was likely to cause a comparable hardness as that of B2 ordered phase
[en] In this note, we are concerned with some metal-oxides mechanical and structural properties. Until a recent date, the main properties that guide the choice of metal-oxides functional materials in PV cells fabrication domain have been restricted to classical ones (Bandgap, electric resistivity, transmission-reflection spectra ...). Recently a great attention has been paid to mechanical and structural performances as a new trend. Hardness measurements have been carried out on different MOx-type oxides. Additional investigations on a particular photovoltaic (PV) functional material: the tungsten trioxide (WO3) have been presented. The results revealed that annealing treatment enhances drastically the mechanical resistance to frontal penetrating solicitation (Hv hardness), without changing the initial opto-thermal performance.
[en] It has been learned that chromium nitride (CrN) performs better than titanium nitride (TiN) under some specific applications. However, the relatively low hardness of CrN still remains a problem. In this study, we tried to increase the hardness of CrN by means of addition of varying content of the third party element Ag/W. The content of Ag/W additive was varied by applying varying levels of currents to the Ag/W targets. Subsequently, a series of tests were conducted to analyze the coatings, including composition and structure analyses, scratch test, Knoop hardness test and wear test. The results showed that the CrN coatings with Ag addition did not show obvious improvement with regard to the hardness and wear performance, while coatings with W addition showed a significant enhancement. Compared with CrN, the W addition led to enhancement in hardness and wear resistance, due to the formation of tungsten nitride (WN) in the CrN coatings. At a W content of 6.8 at.%, the wear was reduced by ∼73%
[en] Examination of thin foils of specimens with various austenitizing conditions by transmission electron microscopy revealed randomly homogeneous precipitation in the ferrite for each experimental condition. Though no interphase precipitation was found in the present study, two types of random precipitation morphologies were identified in the ferrite matrix. One was randomly and homogeneously precipitated carbides of smaller size (<10 nm), and the other was randomly precipitated carbides of larger size (10–30 nm). Transmission electron microscopy results provided evidence that both types of precipitation carbides could be associated with the supersaturation of microalloying elements in the ferrite and austenite, respectively. A higher austenitizing temperature treatment can lead to more microalloying elements dissolving in the austenite such that many tiny carbides precipitation at the low isothermal holding temperature, which is believed to effectively strengthen the ferrite. Vickers hardness data revealed that, in specimens austenitized at 1200 °C and deformed at 900 °C with strains of 10% and 30%, the ranges of hardness distribution were 250–360 HV 0.1 and 310–400 HV 0.1, respectively. For specimens austenitized at 1000 °C and deformed at 900 °C with strains of 10% and 30%, the ranges of hardness distribution were 220–250 HV 0.1 and 220–260 HV 0.1, respectively. Therefore, the average Vickers hardness increased with the austenitizing temperature and deformation strain. However, a wider range of hardness distribution occurred in specimens that underwent treatment at higher austenitizing temperatures. The wider Vickers hardness distribution reflects non-uniform precipitation in each ferrite grain
[en] The effect of cryogenic rolling on the natural aging behavior of a commercial AA7050 aluminum alloy was investigated. Solutionized 10 mm-thick sheets were cryo-rolled to true strains of 0.5, 0.9, 1.1 and 1.4 followed by natural aging (T4 temper) at times ranging from 10 to 1000 h. Light optical microscopy (LOM), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were used to follow the microstructural changes upon processing. Mechanical properties were assessed by Vickers hardness measurements and tensile tests. During natural aging the hardness values increased from 100 HV to approximately 145 HV after 100 h. The strength of the undeformed specimen, naturally aged for 100 h, was much higher than that in the as-quenched state. The yield strength (YS) increased from 130 to 375 MPa (188% increase) and the increment of ultimate tensile strength (UTS) was almost 47% (321–470 MPa). A superior combination of mechanical properties was achieved for the specimen cryo-rolled to a true strain of 0.5 followed by natural aging for 1000 h (YS=611 MPa and 15% total elongation). These results suggest that a combination of cryogenic rolling with natural aging is a useful method for achieving optimized mechanical properties for the AA7050 alloy
[en] Precipitation behavior and its effect on hydrogen embrittlement during tempering process of hot-rolled API steel designed with 0.4 wt% Cr and 0.25 wt% Mo were investigated. The base steel was normalized and then tempered at 650 °C for up to 60 min. The precipitation behavior of the examined steel was explored using transmission electron microscopy (TEM) analysis, and it was found that the precipitation sequence during tempering at 650 °C were as follows: MX+M_3C→MX→MX+M_7C_3+M_2_3C_6. The change of particle fraction was measured by electrolytic extraction technique. At the early stage of tempering, the particle fraction greatly decreased due to dissolution of M_3C particle, and increased after 10 min by the precipitation of M_7C_3 and M_2_3C_6 particles. The particle fraction showed a peak at 30 min tempering and decreased again due to the dissolution of M_7C_3 particle. Vickers hardness tests of base steel and tempered samples were carried out, and then the hardness was changed by accompanying with the change of particle fraction. The sensitivity of hydrogen embrittlement was evaluated through hydrogen induced cracking (HIC) tests, and the results clearly proved that HIC resistance of tempered samples was better than that of base steel due to the formation of tempered martensite, and then the HIC resistance changed depending on the precipitation behavior during tempering, i.e., the precipitation of coarse M_2_3C_6 and M_7C_3 particles deteriorated the HIC resistance.
[en] In this work, 2 vol% carbon nanotubes (CNTs) reinforced aluminum (Al) matrix composites of superior microstructural homogeneity are successfully synthesized using Bc equal-channel angular extrusion (ECAP) route. The key step in arriving at high level of homogeneous distribution of CNTs within Al was preparation of the powder using simultaneous attrition milling and ultra-sonication processes. Microstructure as revealed by electron microscopy and absence of Vickers hardness gradients across the material demonstrate that the material reached the homogeneous state in terms of CNT distribution, porosity distribution, and grain structure after eight ECAP passes. To facilitate comparison of microstructure and hardness, samples of Al were processed under the same ECAP conditions. Significantly, the composite containing only 2 vol% exhibits 20% increase in hardness relative to the Al samples.
[en] This study investigated nano/microsturcture and mechanical/tribological properties in the thixo/rheoformed A356 alloy parts using nano/microindentation and nanoscratch, incorporated with optical microscopy and atomic force microscopy (AFM). As a result, thixo-cast sample exhibited higher mechanical properties than rheo-cast, irrespective of grain size. The reason that mechanical properties of thixo-cast part was higher than that of rheo-cast, was interpreted by the effect of the eutectic region surrounded by the primary α phase on the hardness. It was also observed that shape and distribution of Si particles in the adjacent eutectic region to the primary α-Al phase of the thixo/rheo-cast products were different. By scratching surface of thixo/rheo-cast parts using a nanoindentor, friction forces and coefficients for the primary α-Al and eutectic phases in thixo-cast products were resulted to be higher than those in the rheo-cast. Nanoscratch for the thixo-cast product also revealed a rough and irregular surface compared to that for the rheo-cast, providing the evidence for the effect of eutectic entrapped by primary α-Al phase on mechanical properties
[en] Ultrasonic Additive Manufacturing (UAM) enables the integration of a wide variety of components into solid metal matrices due to the process induced high degree of metal matrix plastic flow at low bulk temperatures. Exploitation of this phenomenon allows the fabrication of previously unobtainable novel engineered metal matrix components. The feasibility of directly embedding electrical materials within UAM metal matrices was investigated in this work. Three different dielectric materials were embedded into UAM fabricated aluminium metal-matrices with, research derived, optimal processing parameters. The effect of the dielectric material hardness on the final metal matrix mechanical strength after UAM processing was investigated systematically via mechanical peel testing and microscopy. It was found that when the Knoop hardness of the dielectric film was increased from 12.1 HK/0.01 kg to 27.3 HK/0.01 kg, the mechanical peel testing and linear weld density of the bond interface were enhanced by 15% and 16%, respectively, at UAM parameters of 1600 N weld force, 25 µm sonotrode amplitude, and 20 mm/s welding speed. This work uniquely identified that the mechanical strength of dielectric containing UAM metal matrices improved with increasing dielectric material hardness. It was therefore concluded that any UAM metal matrix mechanical strength degradation due to dielectric embedding could be restricted by employing a dielectric material with a suitable hardness (larger than 20 HK/0.01 kg). This result is of great interest and a vital step for realising electronic containing multifunctional smart metal composites for future industrial applications