Papers by Keyword: High Hardness

Abstract: In this study, high-hardness transparent silicon nitride was fabricated using liquid-phase sintering. Powders were prepared by adding sintering additives in various ratios, followed by dry pressing at 200 MPa to obtain a circular green body. After forming the green body in the previous process, low-pressure liquid-phase sintering was performed at 1900 °C and 0.7 MPa under a nitrogen atmosphere to produce transparent silicon nitride. According to the test results, the material exhibited a density of 3.148 g/cm³, a Vickers hardness (HV10) of 2100, and a transmittance of 38.5% at a wavelength of 750 nm.

Abstract: The addition of oxygen or nitrogen in titanium alloys increases the hardness by the solid solution strengthening. Spinodal decomposition in titanium alloys is also the way to increase the hardness. This study aimed to reveal the effect of oxygen or nitrogen addition on spinodal decomposition in Ti-10at%V. Ti-10at%V-(0, 1, 3)at%O or N alloys were prepared by arc-melting. They were solution-treated at 1200 or 1300 °C for 0.6 ks and then quenched in iced brine. The solution treated specimens were aged at 375 °C. The increase of hardness was decreased by the oxygen or nitrogen addition in the alloys. The addition of nitrogen more suppressed the age-hardening than the case of oxygen addition. The modulated structure caused by spinodal decomposition in the laths was observed in all the aged specimens. The wavelength of spinodal decomposition of the aged specimens increased with the addition of oxygen or nitrogen, leading to a decrease in age-hardening by spinodal decomposition.

Abstract: Ni-Cr binary alloys containing high amount of Cr demonstrate gamma/alpha-Cr lamellar structure by discontinuous precipitation (DP) reaction from grain boundary. The mechanism of DP reaction is caused by supersaturated Cr in the gamma phase. Supersaturated Cr concentration influences the driving force for the DP reaction and the lamellar spacing. Moreover, the Ni-based alloys with high Cr, containing Al, significantly increase the hardness and strength due to the very narrow lamellar structure. Al addition brings on Ni consumption in the matrix by precipitation of the gamma prime phase. Therefore, Cr supersaturates dramatically in the matrix. The wrought Ni-Cr-Al alloy, Ni-38Cr-3.8Al (mass%) , reaches extremely high tensile strength, which is over 2 GPa, after annealing treatment. Even though chemical composition of Ni-38Cr-3.8Al is simple, the microstructure is complex because it consists of the gamma/alpha Cr lamellar structure with the fine gamma prime particles. Therefore, in this study, we investigated the influence of Cr concentration on the cellular precipitation behaviour. In order to understand the influence of Cr concentration, Ni-34, 36 and 38Cr-3.8Al alloys were prepared. Forged bars were subjected to solution treatment in the gamma single phase region. Subsequently, the alloys were aged from 873K to 1073 K for various times. The cellular precipitation reaction is suppressed by a decrease in Cr concentration, particularly at low temperature annealing treatment condition. The hardness is low in lower Cr concentration alloys in all range of annealing treatment temperature. These results indicate that Cr concentration remarkably affects the driving force for the DP reaction.

Abstract: In this study, the role of chemical soft segment (SS) constructions in thermal and mechanical properties of the elastomers has been investigated by choosing two types of polyol, a polyester and a polyether. Also the effect of the hard segment (HS) chemical construction has been studied. The result showed that compared with polyether based PUs, polyester based PUs have better thermal stability under nitrogen atmosphere. However, the difference for the aging resistance performance of PUs based on polyester and polyether is not obvious without oxidation impact.

Abstract: Shooting nails are mainly applied to fix thin reinforced concrete and steel plate, so the nails should have high hardness and high toughness. Unreasonable heat treatment process could possibly cause too high hardness and decreased toughness, leading to nail cracking and fracture in the course of production and use. Research on heat treatment process through experimental study on the nail determines the reasonable heat treatment process of nail. The feasible quenching heating temperature was 847~840 °C, and the temperature of salt bath during isothermal cooling was 292 °C. Its resultant hardness was 680HV, meeting the requirements of the use of nails. The shoot nail cracking and fracture in the course of use can be avoided effectively. The microstructure of shooting nails after heat treatment showed lower bainite, which contributed to good mechanical properties.

Abstract: Ti–B–C–N and Ti–Si–B–C–N nanocomposite coatings were deposited on AISI 304 stainless steel substrates by DC unbalanced magnetron sputtering from two (80mol% TiB2–20mol% TiC and 40mol% TiB2–60mol% TiC) composite targets in various Si target powers. The relationship among microstructures, mechanical properties, and tribologiacal properties was investigated. The synthesized Ti–B–C–N and Ti–Si–B–C–N coatings were characterized using x–ray diffraction (XRD) and x–ray photoelectron spectroscopy (XPS). These analyses revealed that the Ti–Si–B–C–N coatings are nanocomposites consisting of solid-solution (Ti,C,N)B2 and Ti(C,N) crystallites distributed in an amorphous TiSi2, SiC, and SiB4 matrix including some carbon, BN, CNx, TiO2, and B2O3 components. The addition of Si to the Ti–B–C–N coating led to percolation of amorphous TiSi2, SiC, and SiB4 phases. The Ti–Si–B–C–N coatings exhibited high hardness and H/E values, indicating high fracture toughness, of approximately 35 GPa and 0.098, respectively. Furthermore, the Ti–Si–B–C–N coatings exhibited very low wear rates ranging from ~3×10-7 to ~16×10-7 mm3/(N·m). The minimum friction coefficient of the Ti–Si–B–C–N coatings was approximately 0.15 at low Si target power between 25W and 50W. A systematic investigation on the microstructures, mechanical properties, and tribological properties of Ti–Si–B–C–N coatings prepared from two TiB2–TiC composite targets and one Si target is reported in this paper.

Abstract: Titanium nitride (TiN) coating has excellent properties and has been already used in the various field of industry. But TiN film has problems in the formation process: i.e., low deposition rate and poor thickness of the film. TiN thick coatings can be formed by means of the gas tunnel type plasma reactive spraying in a short time operation. In this study, the fundamental characteristics of this method were investigated by measuring the properties of the titanium nitride (TiN) coatings formed on the traversed stainless steel substrate. Consequently, TiN coatings of 200µm thickness were obtained at P=27kW, within t=5s, and some coating characteristics which depend on the spraying distance, the environmental gas, traverse number etc. were clarified. And the performance of TiN thick composite coating was discussed as a heat resistant TBC.