Papers by Keyword: Surface Hardness

Abstract: Plasma nitriding (ion nitriding) is a plasma-supported thermochemical cementation of steel, during which the hardness of the surface and resistance to wear and fatigue of the material increases due to the formation of a hard layer. The process of plasma nitriding is very variable, which makes it possible to nitride all types of steel, but the result depends primarily on the chemical composition and process tech-nique. In this way, for example, cement, construction, tool steels, high-strength and stainless steels, as well as cast iron, are nitrided. Structural steel belongs to a group of very important and diverse materi-als, it has versatile use in many areas of industry such as machines, vehicles, buildings, bridges, etc. Corrosion of materials is a common phenomenon that cannot be completely eliminated. This degrada-tion is often classified as one of the main reasons for material loss. The article presents the benefit of plasma nitriding on the corrosion resistance of structural steels. Experiments were carried out for select-ed three types of structural steels, on which plasma nitriding was performed and then a corrosion test in a mist of neutral sodium chloride solution. The achieved results confirmed that plasma nitriding has a significant effect on increasing the corrosion resistance of structural steels.

Abstract: This study investigated the effect of degree of availability (d.o.a) of nitrogen and time on increasing the surface hardness of AISI H13 steel using pack nitriding. Urea (46 % N) and ZA (21% N) were selected as a nitrogen source. In this study, hardening was carried out at a temperature of 1030°C then held for 3 hours and continued to quenching with 19 bar nitrogen. Nitriding process used the in-pack process by which the specimens were buried in the urea and ZA powder charged into a nitriding box. Pack nitriding was performed in a vacuum furnace at 600°C for 2, 4 and 6 hours. The surface of nitride-steels was characterized using microhardness tester, SEM/EDS and XRD. After nitriding process, the hardness of AISI H13 steels was increased up to 1648 HV, with the highest hardness achieved by nitriding process of 6 hours and 0.4 d.o.a, in urea media. The nitrogen was dissolved to the steel and induced precipitation of Fe₃N, Fe₂N, and αFe. From the calculation based on Arrhenius equation, the activation energy (Q) of 0.4 and 0.3 d.o.a were 1.381 kCal/mol and 1.455 kCal/mol, respectively.

Abstract: Mortar is another construction medium made of cement, which is mixed with sands and water, and lime is applied to increase the product's longevity. The gypsum renders workability to make mortar or concrete by keeping the cement in plastic state at early age of hydration. The gypsum is called the retarding agent of cement because the gypsum which is mainly used for regulating the setting time of cement. To get the optimal setting time for optimum compressive strength, gypsum in the cement needs to be control. Cement setting time when it hydrates and renders cement paste when combined with water. The objective of this research is to analyze the effect of different amount in Ordinary Portland Cement (OPC). Vicat apparatus was used to analyze the initial setting time of cement paste. Gypsum and clinker were used in production of mortar with the size 50 mm x 50 mm x 50 mm. This research deals with observation of the cement setting time to point out some differences that would effect to strength of mortar. The results reveal that control gypsum with 4% of gypsum has the highest strength as compared to 0% of gypsum and 8% of gypsum. The setting time of cement paste are discussed with respect to their influence on the strength of mortar.

Abstract: This paper introduces the principle of PACVD coating technology, technical characteristics, equipment composition and material characteristics of CrN+DLC. Taking H13 steel as the research object, its surface was treated with CrN+DLC. The microstructure, bonding state and hardness of the interface were studied by means of metallography, SEM, hardness and component distribution of the surface layer. The anti-crack ability and grade of DLC layer were analyzed by studying the shape of crack distribution with Rockwell hardness indentation, and the high quality layer with crack grade of HF1 was obtained. With the dual properties of diamond and graphite of DLC, it can make the die surface have lower friction coefficient, higher hardness, higher impact toughness, better solid lubrication performance and higher corrosion resistance. Surface DLC coating technology provides a new solution to improve the performance of the die.

Abstract: The purpose of the study was to predict the mechanical and toughness properties of Ni-modified alloy steels by adding 1.55%, 1.75%, and 1.95% of Ni-content to the existing Cr-Mo alloy steel of transmission gear material. Typically transmission gears have been working under severe working situations of loads and rotations. Due to these situations, the properties and qualities of gear materials are highly affected consequently, fatigue failure is instigated. So, improving the mechanical and toughness properties of the existing gear material is very vital and compulsory since these properties have a direct impact on gear fatigue failure. Investigations have been done on determining the mechanical and toughness properties of the Ni-modified Cr-Mo alloy steels, through ANN modeling prediction by associating the complex relation of input (chemical composition, tempering temperature) and output parameters (mechanical and toughness properties), and verified by experimental test approaches. Explored these materials property with ANN modeling and experimental test show that the more Ni-content added to the Cr-Mo alloy steel, the higher the ultimate and yield strength can achieve at every instant of tempering temperature. Likewise, fracture toughness, impact toughness, and percent of retained austenite of these materials were also investigated thoroughly as tempering temperature varies. Thus, a 1.55 % Ni-modified Cr-Mo alloy steel has a higher value of both impact toughness and fracture toughness compared with other Ni-modified alloy steels. Similarly, surface hardness was slightly decreased as the amount of Ni-content added increased at each instant of tempering temperature. Lastly, based on both predicted and experimental results, 1.55 % of Ni-modified Cr-Mo alloy steel showed a better combination of mechanical and toughness properties. Keywords: ANN modeling; Yield strength; Ni-modified; Tempering temperature; Fracture toughness; Surface hardness

Abstract: Glass ionomer cement (GIC) is a restorative material that can release flour so as to prevent further caries, biocompatible, translucent, and anti-bacterial, low tensile strength, GIC has limitations that is short working time and cannot be used in areas of teeth that have large masticatory pressure, susceptible to fracture toughness. The addition of silica in GIC is one aspect that needs to be considered because silica has high hardness properties. The source of silica can be synthesized from sea sand which has a silica content of about 98%. This study aims to determine the difference in surface hardness from conventional GIC and GIC by the addition of 5% silica from sea sand. Cylinder-shaped specimens with a diameter of 5 mm and height of 2 mm, totaling 10 specimens, namely 5 conventional type II GIC specimens (control group) and 5 conventional GIC specimens with the addition of silica from sea sand (treatment group). Vickers Hardness Tester is used to measure the value of hardness. Data were analyzed using SPSS with unpaired t test. The results of the data show that there was no significant difference (p> 0.05) between the surface hardness of conventional GIC and GIC with the addition of silica from sea sand.

Abstract: This study presents a prediction study of the surface hardness in surface grinding ASIS 1045 steel. Base on the experimental data on the changes in characteristics of steel in the heat treatment processes, the relationship between the surface hardness and the impacted temperature in surface was found. Besides, the relationship between the cutting temperature and the technology parameters in the grinding was created. The surface hardness was then formulated as a function of the technology parameters in the grinding processes such as the depth of cut, the grinding wheel speed, the workpiece speed, etc. The proposed model was verified by comparing the predicted and measured results of surface hardness. This model can be used to predict the surface hardness when surface grinding.

Abstract: S30408 austenitic stainless steel was treated by using hawking processing which is a type of ultrasonic surface rolling process (USRP). The effects of USRP parameters on surface roughness, surface hardness and corrosion resistance were investigated. Compared with the untreated specimen, the surface roughness and surface hardness is decreased by 87%, the surface hardness is increased by 51% and the corrosion rate reduces after USRP. The surface roughness decreases obviously as the step-size decreases, while the step-size has little effect on the surface hardness and corrosion resistance.

Abstract: Stainless steel is widely utilized due to its higher corrosion resistance and gloss than ordinary steels. However, the applications of stainless steel are still limited because of its low surface hardness. Graphene is a superb material, which has an intrinsic strength of 130 GPa. In this report, the growth of high quality graphene on S304 stainless steel by chemical vapor deposition using acetylene gas as a carbon source is demonstrated. The surface hardness of stainless steel after growing high quality graphene is investigated by nanoindentation technique. High quality graphene can increase the surface hardness of stainless steel from 1.54 GPa to 10.08 GPa. Moreover, the effect of graphene quality on the surface hardness of S304 stainless steel is studied. High quality graphene grown by CVD using acetylene gas as a carbon source can increase the surface hardness of stainless steel about two times more than low quality graphene grown by using methane gas.

Abstract: In orthodontics, nickel-titanium wires are used for teeth alignment and leveling. For leveling the curve of Spee, reversed curve archwires are often used to increase the vertical force needed to correct a deep bite.Objectives: The aims of this study were to investigate and compare the mechanical properties (unloading force, stiffness, springback, and surface hardness) of the pre-formed plain and reversed curved NiTi archwires.Materials and Methods: NiTi wires of dimensions 0.016x0.022 inch were divided into two groups, Group 1 - plain and Group 2- reversed curve NiTi archwires. For each type of the archwire, load-deflection curve obtained from a three-point bending test, performed by a Texture Analyser (TA.XT.plus, Stable Micro System, United Kingdom) with 5 kg load cell at room temperature, was used to analyze unloading force, springback, and stiffness. Surface hardness was measured by Vickers micro-hardness tester. Kruskal-Wallis test was used to analyze the variables of this study.Results: The results showed that the unloading force of each deflection point of the reversed curve NiTi archwire was more than the plain archwire. The means of unloading force, stiffness, and springback were 2.42 N, 2.76 N; 0.28 N/mm, 0.49 N/mm; and 2.94 mm, 2.98 mm for the plain archwire and reversed curve NiTi archwire, respectively. The properties of reversed curve NiTi archwire were significantly higher (p<0.05) than the plain NiTi archwire, except the springback. The surface hardness of the plain archwire was significantly higher (p<0.05) than reversed curve NiTi archwire in each segment.Conclusion: The reversed curve NiTi archwire had more unloading force and stiffness than plain NiTi archwire. For the correction of deep curve of Spee in orthodontic treatment, clinicians must be aware of the vertical force needed during intrusion of lower incisors or the wires should be used in the later leveling and aligning stage.