Resumo em Inglês:

For TA15 Ti-alloy large-scale component, isothermal local conventional forging (ILCF) combined with subsequent heat treatment provides a feasible approach to obtain a tri-modal microstructure with attractive comprehensive performance. However the tri-modal microstructure characteristics and evolution laws in the first and second loading zones are lack of understanding. In this paper, the effects of ILCF conditions on the tri-modal microstructure in the first and second loading zones were investigated under given subsequent heat treatment and the reasonable ILCF conditions were proposed. As forging temperature increases, in both loading zones the content and aspect of equiaxed αp decrease obviously while the content and thickness of lamellar αs increase. The content and thickness of lamellar αs in the second loading zone are higher. Forged at a moderate strain rate of 0.1s-1, the content of lamellar αs is higher, and the differences in the content and morphology of constituent phases in both loading zones are relatively small. Compared with air cooling after forging, water quenching result in more and disordered lamellar αs, and less differences in obtained tri-modal microstructure in the first and second loading zones. Under three loading passes, the uniformity of tri-modal microstructure in the first and second loading zones is better.

Resumo em Inglês:

This work reports the formation of nanoprous Pd with tunable pore size and high stability by dealloying Pd30Cu40Ni10P20 metallic glass. The results show that lower dealloying temperature results in smaller pore size while the dealloying duration does not cause distinct change in the porous structure, even at an ambient dealloying temperature. The glassy structure and the multiple components in the precursor alloy are attributed to the hindered diffusion of Pd atoms and a slow coarsening rate of the nanoprous structure. The fully dealloyed porous sample with the smallest average pores size of 10 nm exhibit much higher catalytic activity when compare with the commercial Pd/C catalysts while the specimen with an average pores size of 13 nm shows the highest catalytic stability among the fully dealloyed alloys.

Resumo em Inglês:

Isothermal compression tests of Ti-5553 (Ti-5Al-5V-5Mo-3Cr) alloy, produced by a fast consolidation approach from blended elemental powder mixture, were performed on a Gleeble® 3800 thermal-physical simulator to investigate its hot deformation behaviour. The samples were compressed in a wide temperature range from 700 ºC to 1150 ºC and a moderate-high strain rate of 1 s-1, with the sample deformation degree of 30%, 50% and 70%, respectively. Flow instability occurred when the deformation temperature was less than 900 ºC. Dynamic recovery (DRV) accompanied by dynamic recrystallization (DRX) become the dominated mechanisms at the medium temperature range between 900 ºC and 1000 ºC, while almost only DRV features could be observed at high temperature (1050 ºC ~ 1150 ºC). Moreover, α phase globalization could be identified in the alloy deformed in (α+β) region. DRV, DRX, α globalization and the transformation of α to β phase were promoted with the increasing deformation degree.

Resumo em Inglês:

An hypereutectic aluminium alloy with a composition of 16-18wt%Si, 4-5wt%Cu, 0.45-0.65wt%Mg, 0.3wt%Nd and Al balance (A390-0.3wt%Nd alloy) was processed by extrusion and aging at 200ºC for 10 hours. The effect of the thermomechanical processing and heat treatment on microstructure and mechanical properties was investigated for A390-0.3wt%Nd alloy. It was shown that the eutectic structure disappeared after the processing and heat treatment. In the meantime, the morphology of Al(Si,Mg) solid solution was transformed from dendritic to equiaxed and the Si particles were refined to have fine sizes of 1-10µm and dispersed in the Al(Si,Mg) matrix. Some of the Si particles became globular in shape, which can reduce stress concentration. The tensile strength of the A390-0.3wt%Nd alloy increased by 14.8% (211MPa to 242MPa) after extrusion and aging, and the elongation to fracture increased significantly from 0.5% to 13.3%. Thus, the mechanical properties of extruded and heat-treated A390-0.3wt%Nd alloy were improved after the extrusion and aging. The fracture mode is transformed from brittle fracture of as-cast alloy to ductile fracture of extruded and heat-treated alloy.

Resumo em Inglês:

Hydrogen, which is a harmful element, has a great effect on the mechanical properties of steel, should be removed during the steel manufacture process. The evolution of hydrogen content in steel during electroslag remelting process is experimentally investigated. The results show that during the electroslag remelting process, the hydrogen content in steel firstly increases steeply to maximum, then decreases to minimum and reaches the equilibrium. For a prefixed slag composition, the final hydrogen content in steel depends on the initial hydrogen content and the atmospheric moisture. When the electroslag remelting is operated under the argon protected atmosphere, the hydrogen in steel increased slightly. With the increase of the atmospheric moisture, the hydrogen content in steel increased significantly, and the larger atmospheric moisture is, the more significant influence on the hydrogen content in steel is. Moreover the mathematical formula to predict the hydrogen content in steel from the initial hydrogen content and the atmospheric moisture is derived: w%He=0.359w%HS+0.016pH2O/pΘ+0.525 It could be used to forecast the final hydrogen content in ESR ingot.

Resumo em Inglês:

Duplex Ni-P-TiO2/Ni-P coatings were electrodeposited onto brass substrates. High phosphorus Ni-P coatings were plated as the inner layer to improve the corrosion resistance, while low phosphorus sol-enhanced Ni-P-TiO2 coatings were deposited on the top to strengthen the mechanical property. The microstructure, morphology, mechanical property and corrosion resistance of coatings were investigated systematically. The results show that duplex coatings exhibit both excellent mechanical property and good corrosion resistance. The hardness was further improved from ~545 HV50 of duplex Ni-P/Ni-P coating to ~622 HV50 of duplex Ni-P-12.5mL/L TiO2/Ni-P coating, while the hardness of single Ni-P coating was only ~387 HV50. The corrosion resistance of duplex coatings improved significantly by adding a suitable amount of TiO2 sol. Duplex Ni-P-12.5mL/L TiO2/Ni-P coating presented the highest corrosion resistance. However, adding excessive quantities of sol (more than 12.5mL/L) caused nanoparticle agglomeration and created a porous structure in the outer layer, deteriorating the properties of coatings.

Resumo em Inglês:

The comparisons of mechanical properties and fracture behaviour between as-consolidated PM Ti-5553 alloy and as-cast IM Ti-5553 alloy were investigated through tensile, fracture toughness and impact toughness tests in this research. The slightly higher strength but much higher ductility and toughness can be identified in IM alloy specimens, which is also confirmed by the fracture behaviour of the specimens after mechanical tests. IM alloy specimens always exhibit the ductile dimple fracture mechanism in the different tests, while the fracture mechanism of PM alloy specimens indicates a high loading rate sensitivity, changing from the mixed ductile-brittle quasi-cleavage fracture into the brittle cleavage fracture mechanism accompanied by the remarkable decrease of impact toughness. The relatively low mechanical properties, especially the ductility and the brittle fracture behaviour of as-consolidated PM Ti-5553 alloy, are mainly explained by the differences in the initial microstructures between these two alloys.

Resumo em Inglês:

The microstructure evolution of Fe-19Mn-8Cr-1Co-0.2Si (wt.%) alloy and Fe-19Mn (wt.%) alloy during cold rolling and its effect on the damping capacity of the two alloys were investigated. It was shown that the damping capacity of the two alloys was enhanced significantly owing to the deformation-induced ε-martensite and stacking faults. The Fe-19Mn-8Cr-1Co-0.2Si alloy exhibited an accelerated phase transformation from γ-austenite to ε-martensite due to a higher content of retained γ-austenite and larger grain sizes compared with the Fe-19Mn alloy, resulting in a higher maximal increment of damping capacity in this alloy caused by deformation. It was observed that no twinned ε-martensite was generated in the Fe-19Mn-8Cr-1Co-0.2Si alloy during cold rolling, resulting in a remarkable increase in the volume fraction of α'-martensite owing to no impediment to ε → α' transformation, hence the deterioration of damping capacity was slow because the α'-martensite weakened the pinning effect of dislocations on damping sources. In addition, new damping sources were provided due to the occurance of γ-austenite twinning in the Fe-19Mn-8Cr-1Co-0.2Si alloy.

Resumo em Inglês:

Macro- and micro-texture of Fe-2.1 wt.% Si alloy sheets were investigated and analyzed by X-ray diffraction and electron backscattered diffraction techniques. A Goss ({110}<001>) component accompanied by extremely weak γ (<111>//ND, normal direction) fiber is successfully formed through the sheet thickness after primary recrystallization and considerable grain growth. Goss grains mainly nucleate at shear bands in various deformed matrices with orientations spreading from <112>//ND to <332>//ND fibers. The formation of dominant Goss recrystallization texture through the thickness can be attributed to the suppression of the nucleation at grain boundaries of γ deformed matrices and the promotion of the nucleation at shear bands in various deformed matrices, based on optimization of the initial texture and microstructure and the applied processing parameters.

Resumo em Inglês:

Selective laser melting (SLM) is an additive manufacturing technique which permits fabrication of three dimensional parts by selectively melting consecutive layers of metallic powder. This allows the production of parts with high geometrical complexity. Titanium alloy Ti-6Al-4V (Ti64) is widely used in industry due to its high strength-to-mass ratio, corrosion resistance and biocompatibility. SLM increases the application range of Ti64 because of its flexibility for prototyping any part and its low material waste. Nitriding is a diffusion-based thermo-chemical treatment for interstitial hardening of the surface of Ti64 alloy products. This study characterized the fatigue behaviour of SLM-produced Ti64 nitrided and annealed bars in as-built and machined surface conditions. The surface of the SLM-produced Ti64 parts after gas nitriding showed high values of micro-hardness up to 550 HV just below the surface. Fatigue testing was performed to assess the materials fatigue strength and fractographic imaging was used to examine fracture surface and nitride layer characteristics. Nitriding was found to reduce the fatigue strength of the samples to a similar level irrespective of being in the as-built or machined condition. The effect of nitriding on crack initiation and growth at various stress levels under fatigue loading was investigated.

Resumo em Inglês:

Microstructures and tensile properties of a hot forged Ti−22Al−23Nb−3V−Y alloy were investigated systematically. Different heat treatments were performed to adjust the wrought microstructure to optimize tensile properties. It was found that features of O phase precipitates and its volume fraction was rather sensitive to the cooling rate after the solution. The volume fraction of primary lamellar O phase increased from 19.65% by solution treatment to 36.30% by annealing with furnace cooling and up to 100% by annealing with a controlled slow cooling rate of 1 ºC/min. Meanwhile, the width of the lamellar secondary O phase increased. Fine acicular second O phase contributed to strengthening, while the coarsen primary ones were favorable to the ductility. The solution & aging treated microstructure exhibited a good tensile strength of 1100 MPa and an acceptable ductility of 8% at room temperature, by contrast, annealing at 950 ºC with a controlled slow cooling rate gave rise to a higher elongation of 12%, but a relatively low strength of 960 MPa.

Resumo em Inglês:

4.5 wt.% Si grain-oriented electrical steel sheets were successfully produced by hot rolling, normalizing, warm rolling and annealing, and texture evolution was investigated using macro- and micro-texture analysis. It is found that the recrystallization texture of sheets is very sensitive to the warm rolling reduction, and 83-87% warm rolling reductions are more favorable to η texture (<100>//RD, rolling direction) evolution during secondary recrystallization, and consequently the magnetic induction B8 is significantly improved to 1.69-1.70 T in this rolling reduction range. The decreased B8 in the 89% warm rolled sheet is ascribed to the obviously decreased primary recrystallization η fiber, which leads to the insufficient quantity of η grains in the early stage of abnormal grain growth. The results obtained in the current work can provide an efficient way to improve the recrystallization texture of 4.5 wt.% Si grain-oriented electrical steel sheets.

Resumo em Inglês:

Based on the principle of dilute solution approximation, a phase field model for dendritic growth during the non-isothermal solidification process was proposed by coupling the phase field, concentration field and temperature field, and was adopted to investigate the dendritic growth of Al-Cu binary alloy during the non-isothermal solidification process. Also, the simulations of free dendritic growth in an undercooled melt of Al-4.5%Cu binary alloy with different perturbation intensity and anisotropy were carried out by the present phase field model. The results show that during the non-isothermal solidification process of Al-4.5%Cu binary alloy, the dendrite grow into undercooled melt with the solute rejection and latent heat release at the front of solid/liquid interface, and the solute enriches at the dendrite root and high temperature appears at the dendritic growth front. With the increase of perturbation intensity, the dendritic growth becomes more developed and more branches appear. Moreover, the anisotropy coefficient also has a great effect on the dendritic growth, and the growth speed of dendrite increases with the increase of anisotropy coefficient.

Resumo em Inglês:

HA/ZnO coatings with varying content of ZnO were fabricated on Ti-6Al-4V substrate to enhance its bioactivity and antibacterial ability. The main phases are identified as CaTiO3, Ca3(PO4)2, ZnTiO3 and CaO. The coatings with higher ZnO content presented smaller grain size, resulting in a higher surface free energy and better wettability. Consequently, the mineralization of the ZnO/HA coatings, especially for the higher ZnO content samples were improved, indicating better enhanced in vitro bioactivity. The ZnO-HA coated Ti-6Al-4V presented better corrosion resistance than bare Ti-6Al-4V substrate. Furthermore, better corrosion resistance was obtained by increasing ZnO content in the precursor. The antimicrobial ratio of all coatings was approximately 100%, indicating the ZnO doped HA coatings presented excellent antibacterial ability.

Resumo em Inglês:

Naked Co68.25Fe4.5Si12.25B15 metal fibers with diameter from 25 µm to 100 µm are produced by melt extraction method. Significant diameter dependence of magnetic properties is studied. Their microstructure and magnetic properties of hysteresis loops and giant magneto impedance (GMI) effect at frequencies from 0.1MHz to13MHz are investigated. The results show that the coercivity increases with the diameter of fibers and the GMI effect is best in fiber with a diameter of 35µm. It is found that the cooling rate of solidification decreases with the increase of fiber diameter. And fibers are amorphous with the diameter of 50µm and there are nanocrystallines in fibers with a diameter of 85µm. The grain boundary blocks the magnetization process which makes lower circular permeability, larger coercivity and lower field sensitivity of GMI effect. The original microstructure of Co-based fibers decides their magnetic properties. Therefore, material design is important to improve the GMI effect in magnetic field sensor making.

Resumo em Inglês:

The effects of the sintering time on the electrical properties and the positive temperature coefficient of resistance (PTCR) effect of Ba1.006(Ti1-xNbx)O3 (BTN) ceramics were investigated, which were sintered at 1190 ºC for 0.5-6 hours in a reducing atmosphere and then re-oxidized at 800 ºC for 1 hour. The results indicated that the sintering time affected the electrical properties and the PTCR effect of the multilayer BTN samples, whose room-temperature resistance decreased with an increase of the sintering time at same sintering temperature of 1190 ºC. However, the resistance jump first increased and then reduced as a function of the sintering time. Furthermore, The BTN ceramics exhibited a pronounced PTCR effect, with a resistance jump greater by 3.6 orders of magnitude, along with a low RT resistance of 0.14 Ω at a reoxidated temperature of 800 ºC after sintering at 1190 ºC for 2 h in a reducing atmosphere. In addition, the activation energy of samples obtained at different sintering times had also been investigated.

Resumo em Inglês:

The giant magneto impedance, GMI, effect of Co-based metallic fibers prepared by melt-extracted technology is investigated under different bias direct electrical current Ib. The GMI curves have single peaks which are symmetric about zero field at and below 1MHz. However, the bimodal GMI curves which have asymmetric peaks are observed when Ib is over 2mA at 0.1MHz. And asymmetric GMI, AGMI, effect is also appeared at 1MHz when Ib just is 1mA and the field sensitivity of GMI effect is increased 5.6 times. The GMI effect and magnetization process is affected by the bias magnetic field profoundly induced by Ib, which is correlated with the outer shell domain structures with circumferentially magnetization easy axis existed in the outer shell of Co-rich magnetic wires with low and negative magnetostriction. Below 1 MHz, only if the bias current is over 1.5mA which induces a magnetic circumferential magnetic field is above the coercivity of 14.4A/m, the circumferential magnetization and GMI effect can experience the bias magnetic field effect. Above 1MHz, the skin effect gets stronger and significantly decreases the total participants of circular magnetization process in the fibers and consequently, the circular outer shell magnetization process gets much sensitive to circular bias magnetic field. AGMI effect with high field sensitivity is realized due to the bias current.

Resumo em Inglês:

The influence of the Nb5+-doped content and the doping CaCO3 on the electrical properties and the microdefects of BSTN ceramics by Positron Annihilation Techniques were studied, which were fired at 1350 ºC for 2 hours in air. The PTCR characteristics in the BSTN samples were also investigated. Moreover, the information on microdefects in BSTN ceramics was demonstrated by coincidence Doppler broadening spectrum measurements and positron annihilation lifetime spectra. Meanwhile, the influence of the defects on the electrical properties of the ceramics was also revealed. Furthermore, the critical donor-dopant content was 0.4 mol%, which corresponding room-temperature resistivity and the resistivity jumping ratio was 714.3 Ω·cm and 2.77 × 102, respectively. In addition, the average positrons annihilate lifetime t of the BSTN ceramics was investigated as well.

Resumo em Inglês:

Mg-3Zn-0.5Sr-xCa(wt.%) (x=0, 0.2, 0.5) alloys were fabricated by casting and hot extrusion. X-ray diffraction (XRD) and optical microscopy observation showed that the microstructure of Mg-3Zn-0.5Sr-xCa alloys was composed of α-Mg matrix and Mg17Sr2 phase precipitated along grain boundaries. The tensile strength of the alloy increased from 255MPa to 305MPa with increasing Ca content from 0 to 0.5wt%, but the elongation to fracture of the alloys was 19.45%, 28.7% and 15.2% respectively, indicating that coarse precipitation increased the risk of crack initiation and propagation along the grain boundaries leading to reduced ductility of Mg alloys. The polarization curves revealed that Mg-3Zn-0.5Sr-0.2Ca has the highest corrosion potential and the lowest corrosion current density indicating the optimum corrosion resistance. In cytotoxicity test, Mg-3Zn-0.5Sr-xCa alloys were harmless to mouse osteoblastic and Mg-3Zn-0.5Sr-0.2Ca alloy exhibited optimal biocompatibility.

Resumo em Inglês:

The microstructure and texture distribution of a Ti-1023 forged disk were investigated by scanning electron microscopy and synchrotron-based high-energy X-ray diffraction. The finite element method was used to simulate temperature and strain distribution in order to investigate the relationship of the α/β forging process with microstructure and texture distribution. A bimodal microstructure and rolling textures with large inhomogeneity were observed in the disk. A plate-like and a necklace-like morphology and volume fraction variations of the primary α phase were observed in different regions with different forging conditions, such as temperature, deformation, position, and high density of flow lines. Texture sharpness distribution of the β phase was in good agreement with the strain distribution, which suggests deformation may play the most important part in the texture inhomogeneity. A weak cube texture was obtained near the center of the disk, and fiber textures were found near the rim of the disk. The primary α phase also exhibited a transverse texture, which is favored by large deformation.

Resumo em Inglês:

In this work, we investigated the effect of yttrium(Y) on microstructure, the mechanical and corrosion properties and the cytotoxicity of Zn-1.5Mg-xY(x=0, 0.2, 0.5wt%) alloys prepared by casting and extrusion. The results showed that the microstructure of extruded Zn-1.5Mg-xY alloys consisted of α-Zn matrix, Mg2Zn11 particles and Y containing blocks. The tensile strength and compressive strength of Zn-1.5Mg-xY alloys improve with the increase of Y content. Alloying with Y also had an impact on the corrosion resistance of Zn-Mg alloys. In terms of toxicity, the cells cultured in the leachate of Zn-1.5Mg-xY alloys with concentrations of 25% and 50% showed good growth morphology with the relative proliferation rate (RGR) values being greater than 100% and the cytotoxicity level being 0, the addition of Y has little effect on the compatibility of alloy with cells.

Resumo em Inglês:

Recrystallization kinetics of Fe-3%Si with initial grain size 296~839µm at the temperature range 1223~1423K, strain range from 0.51 to 0.92, strain rate range 5~80s−1 was studied by isothermal compression test using Gleeble-2000. The effect of strain, strain rate, initial grain size and annealing temperature on the recrystallization kinetics were discussed. Avrami equation was used to describe the static recrystallization kinetics. Moreover, the effect of initial grain size and annealing temperature on the exponent in Avrami equation was discussed and the reason of the exponent deviating from the theory value is owed to the effect of static recovery. In all the experimental range the static recrystallization kinetics can be well predicted by Avrami equation.

Resumo em Inglês:

Warm rolling of medium Mn steel is a promising technology to meet the needs of vehicle weight reduction and energy conservation while ensuring the safety for passengers. In this study, a novel Nb-Mo microalloyed 6.6Mn steel was subjected to a series of warm rolling tests at temperatures ranging from 630 to 690 ºC, based on the thermodynamic-based prediction of inter-critical annealing using a Thermo-Calc software. As a comparison, a conventional multi-stage thermo- mechanical process involving hot rolling, cold rolling and inter-critical annealing was carried out as well. The optimal rolling temperature parameters for warm rolling was explored through tensile tests and the detailed microstructural characterization. The experimental results show that the microstructure and mechanical characteristics strongly depended on the warm rolling temperature. A better combination of UTS and TE products (~32.0 GPa·%) was achieved in the 660ºC-warm-rolled specimen, which is much higher than 12.3 GPa·% for the hot formed 22MnB5 steel and is also comparable to 38.3 GPa·% for the annealed cold-rolled specimens.