Effects of Zr/(Zr+Ti) Molar Ratio on the Phase Structure and Hardness of TixZr1−xN Films

TixZr1−xN hard films with Zr/(Zr+Ti) molar ratios from 20% to 80% were prepared by multi-arc ion plating using any two of elemental Ti, elemental Zr, and TiZr alloy targets. The as-deposited TixZr1−xN films displayed similar surface and fracture cross-section morphologies and thicknesses. The effects of Zr/(Zr+Ti) molar ratio on the phase composition, preferred growth orientation, and hardness of the films were discussed. The results showed that the as-deposited films had a face-centered cubic structure and exhibited the typical characteristics of substitutional solid solutions. The lattice constant of the films increased monotonically with increasing Zr/(Zr+Ti) molar ratio. Two preferred growth orientations, corresponding to the two hardness peak values, occurred symmetrically at Zr/Ti molar ratios of 40:60 and 60:40. An inflection point with a small reduction in hardness was observed at the Zr/Ti molar ratio of 50:50.

Can Sub-zero Treatment at −75 °C Bring Any Benefits to Tools Manufacturing?

: Vanadis 6 ledeburitic tool steel was subjected to sub-zero treatment at −75 °C for different durations, and for different subsequent tempering regimes. The impact of these treatments on the microstructure, hardness variations, and toughness characteristics of the steel was investigated. The obtained results infer that the retained austenite amount was reduced to one fourth by sub-zero treatment (SZT), and the population density of add-on carbides was increased by factor of three to seven, depending on the duration of SZT. Tempering always reduced the population density of these particles. A hardness increased by 30–60 HV10 was recorded after sub-zero treatment but tempering to the secondary hardness peak induced much more significant hardness decrease than what was established in conventionally quenched steel. The flexural strength was not negatively influenced by sub-zero treatment at −75 °C while the fracture toughness tests gave worse values of this quantity, except the case of steel tempered to the secondary hardness peak.

Effect of Zn/Mg Ratios on Microstructure and Stress Corrosion Cracking of 7005 Alloy

The effects of different Zn/Mg ratios on the microstructure, mechanical properties and resistance of stress corrosion cracking of peak-aged 7005 aluminum alloy were investigated. It was found that the Zn/Mg ratio played a very important role in controlling the aging time, the electrical conductivity of the hardness peak point and the resistance of stress corrosion cracking of the alloy. With the increase of Zn/Mg ratio (wt. %), the time taken by the alloy to achieve the peak hardness value gradually increases aging at 120 °C. When the Zn/Mg ratio is in the range from 2.27% to 2.62%, the precipitate phase of the alloy after peak-aged is mainly dominated by smaller disc-like η’ phase and GP I (Guinier Preston) zones, the grain boundary precipitates are slender and continuous and the PFZ (precipitate free zones) is narrow. However when this value is in the range from 3.01% to 4.08%, precipitation phase in matrix of the alloy is mainly composed of short-rod η′ phase and GP II zones, the precipitation phases within the grain boundary are large and distribute intermittently and the PFZ is narrower. The results of SSRT (slow strain rate tests) show that when Zn/Mg ≥ 3.61, the 7005 aluminum alloy at peak-aged has good resistance of stress corrosion cracking in 3.5% NaCl + 0.5% H2O2 aqueous solution. However, when Zn/Mg ≤ 3.01, the strength of the alloy sharply decreases in 3.5% (wt. %) NaCl + 0.5% (wt. %) H2O2 aqueous solution.

Effect of cooling rates on T6 Treatment of B390 Aluminium-Silicon Hypereutectic alloys

This research aimed to study an effect of cooling rates on T6 treatment process of B390 aluminium hypereutectic alloy. B390 casting samples were casted with pouring temperature of 710°C and solidified in three different cooling rates of 33.33, 28.60 and 22.22°C/s, respectively using three metal moulds. After that samples were subjected to T6 treatment: solution treated at 510°C for 30 min and aged at 200°C at various times. However, after ageing, hardness values of as-casted samples reduced with increasing cooling rate. It was found that the specimen cooled with the highest cooling rate exhibited the highest hardness. Peak hardness values of samples cooled with cooling rate of 33.33, 28.60 and 22.22°C/s after ageing obtained from ageing time of 3, 6 and 8 hour, respectively. Furthermore, the result showed that morphology of primary silicon, eutectic silicon and Ali5(Mn, Fe)3Si2 phase presented in the aged specimen cooled with the highest cooling rate exhibited more globular, finer and distributed more evenly compared with the slower cooled samples. It can be concluded that rapid cooling rate increases concentration of a-solid solution resulted in shorter aging time.

Aging Behavior of A356.2 with Yb Modified

The effect of aging treatment on the aging hardening of 0% Yb and 0.4% Yb modified A356.2 alloy was investigated by hardness measurements and optical microscope. In this work, A356.2 was first subjected to 535°C for 5h and then subjected to 150°C, 180°C for 2h-12h hours. Results show that during aging process, there was a hardness peak along the increasing of aging temperature and time. With increasing aging progress, the morphology of Si phases became shorter and spherical. After optimum time, Si phases was coarse and the dendritic grain was broken. The peak-aged of unmodified alloys was 150°C for 10h and 180°C for 6h，and corresponding hardness values were 62.35HB and 77.10HB, respectively. With Yb addition, the hardness reached 87.58HB and 98.28HB on peak aging of 150°C/8h and 180°C/ 6h, respectively. The greatest degree of hardness was increased by 40.46% and 27.47%, combined with no Yb addition. XRD shows the interplanar crystal spacing of A356.2 with 0.4% Yb addition, which was larger than fresh A356.2 alloy. When adding 0.4%Yb under 180°C for 6h aging progress, the ultimate tensile strength was 284 MPa 12.7% increasing compared with former work.

Effect of Ti on the Structure and Properties of Cu-15Ni-10Mn Alloy As-Cast Smelted at Atmosphere

Cu-15Ni-10Mn alloy as-cast, which smelted at atmosphere, has a typical dendrite structure in Ni segregation characteristics. The content of Ni is higher on dendrite arms spacing than on the dendrite arms, but the content of Mn is less than on the trunk. Due to the Mn oxides easily, the processing performance of alloy as-cast cant meet the requirement of metalworking. The gas content of ingots can be reduced by adding a small amount of zinc during smelting, and the metalworking features can be improved by adding trace Ti that will refine the arms of alloy. The research results show that the grains of Cu-15Ni-10Mn alloy as-cast can be refined by tiny amount of Ti. The grain size decreases with the increase of the content of Ti, the branches size of alloy adding 0.2% Ti is about 30μm that is only 49.4% the size of the alloy without Ti. Titanium, copper and Nickel can form compounds of CuNi2Ti. The hardness peak of alloy with 0.2%Co is 114Hv that is 8% higher than the alloy without Ti. The electrical conductivity of Cu-15Ni-10Mn alloy as-cast waves not clearly.

Experimental Correlation for the Effect of Metallurgical Parameters on the Hardness of 356 and 319 Aluminum Alloys Using Minitab Software

The present study was undertaken to investigate the effect of metallurgical parameters on the hardness and microstructural characterisations of as-cast and heat-treated 356 and 319 alloys, with the aim of adjusting these parameters to produce castings of suitable hardness and Fe-intermetallic volume fractions for subsequent use in studies relating to the machinability of these alloys. Hardness measurements were carried out on specimens prepared from 356 and 319 alloys in the as-cast and heat-treated conditions, using different combinations of grain refining, Sr-modification, and alloying additions. Aging treatments were carried out at 155 °C, 180 °C, 200 °C, and 220 °C for 4 h, followed by air cooling, as well as at 180 °C and 220 °C for 2, 4, 6, and 8 h. Peak hardness was observed in 356 alloys when aging was carried out at 180oC/4h. In the case of unmodified or modified 356 alloys containing mostly α-Fe intermetallics, aging at 180 °C up to 8h produced a sharp rise in hardness during the first two hours of aging, followed by a broad peak or plateau over the 2-8 h aging period. Aging at 220 °C revealed a hardness peak at 2h aging time for both 356 and 319 alloys. Addition of Mg to unmodified or modified 319 alloys produced a remarkable increase in hardness at all aging temperatures. This may be explained on the basis of the combined effect of Cu-and Mg-intermetallics in the 319 alloys, where hardening during aging occurs by the cooperative precipitation of Al2Cu and Mg2Si phase particles.[, ] For 356 and 384 alloys, the Mg-containing 319 alloys (~same Mg concentration as in 356 alloys) displayed higher hardness values than the 356 alloys for the aged condition, where hardening occurs by cooperative precipitation of Al2Cu and Mg2Si phase particles in 319 alloys compared to only Mg2Si precipitation in the case of 356 alloys.

Structural and Hardness Gradients in the Heat Affected Zone of Welded Low Carbon Martensitic Steels

Welding of low carbon martensitic steels with yield strengths above 690 MPa requires careful attention to the welding procedure to avoid hydrogen assisted cold cracking (HACC) and to minimise degradation of the mechanical properties of the weldment. Investigations of the microstructural and hardness gradients in the heat affected zone (HAZ) of these types of steels revealed that the peak hardness does not occur in the grain coarsened heat affected zone (GCHAZ) adjacent to the fusion boundary, as normally observed for ferritic steels, but is displaced towards the grain refined region (GRHAZ). This phenomenon, referred to as the displaced hardness peak (DHP) effect, is considered to arise when the hardenability of the steel is sufficiently high to produce the same microstructure in the both the GC and GR heat affected zones, but the enhanced structural refinement of the GRHAZ increases the hardness and strength above that of the GCHAZ. Implications relative to the susceptibility of the weldments to HACC are discussed.

The Study of Interfacial Reactions and Mechanics Properties for Die Casting (Al63Cu25Fe12)p /AZ91 Composites

A novel Mg-based composites (Al63Cu25Fe12)p /AZ91 was prepared by pressure die casting protected by CO2/SF6 condition. The–200mesh quasicrystalline powders were poured into the molten AZ91Mg alloy and then rapidly stirred for 30 min in 720°C. The phases and phase transformation in the process of heat treatment for Al63Cu25Fe12 powder, and the reaction between matrix metal AZ91 and Al63Cu25Fe12 particle has been investigated using Scanning Electron microscopy (SEM) and Energy spectrum diffraction analysis technology（EDAX）. It is shown that i-phase decomposed in process of stir and the Cu atoms diffuse from powders into the matrix and combine with Mg and Al in the matrix, which produces metallic-compound dispersing along the grain boundary. The Mg atoms diffuse into the powders and substitute the Cu atom sites. After heated with solution and ageing, composites of (Al63Cu25Fe12)p /AZ91 is different from magnesium alloy, they need less time to get the ageing hardness peak. The mechanics properties of composites have been improved outstandingly by hot-extruded and treatment of solution and ageing, the tensile strength σb is from 189.54MPa up to 359.38MPa. However, because of their brittleness, the plasticity of composites decreased.