Papers by Keyword: Microhardness

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Authors: Krishnamorthy Raghukandan, P. Tamilchelvan, N. Meikandan
Abstract: Explosive cladding is a non-conventional, solid-phase bonding technique in which bonding between two plates is produced by their high velocity collision induced by the use of explosives. Attempts were made to explosive clad Titanium-Stainless steel (SS 304 L) plates (3.5 and 3.0 mm thick respectively). The experiments were designed to analyze the bonding interface parallel to the detonation direction. The presence of intermetallics, caused by the melting at the interface due to kinetic energy dissipation, was observed in some locations. The process parameters of the explosive welding of Titanium-Stainless steel combination are defined using the microstructural observations, microhardness at the interface, the results of X-ray diffraction study. A weldability window is also constructed for explosive welding of Ti /Ss.
Authors: Shi Nan Li, Hui Chen, Yan Jie Zhang, Zhang Yu Gao, Li Zhen Liu, Bing Ma, Lu Ning Yu
Abstract: Procedures of thermal diffusion (TD) process are carried out on two specimens of Cr12MoV steel using the same salt bath formula. For the two specimens, the beginning V concentration, V concentration at the time specimen is added, are different, the level of which is controled by changing the interval between the specimen are added and the time reducing agent of Al meeting with vanadizing source of V2O5. The interval for Specimen 1 and Specimen 2 are 10 and 30 minutes respectively. Consequently, different changes are happened on the surface of the substrates. The microstructures of coatings are observed by optical metallographic microscope and SEM/EDS, the hardness are tested by Vickers micro-hardness tester. Results show that: VC coating formed on Specimen 2 is of better performances than Specimen 1, microhardness of Specimen 2 reaches as much as 2400HV. It can be concluded that level of V concentration at the beginning of TD process is a vital factor for the forming of VC layer.
Authors: Y.Z. You, D.I. Kim, H.G. Chun
Abstract: The near surface of the H13 steel was implanted by using Plasma immersion ion implantation (PIII) system at constant bias voltage of −20 kV with varying nitrogen (N+ ) ion dose (3, 6, 9, 12, 15×1017 ions/cm2 ). The surface properties of the N+ ion implanted steel were investigated by measuring the microhardness, wear loss and friction coefficient. As increasing N+ ion dose (12×1017 ions/cm2), both wear property and surface hardness were increased. However, these properties were decreased as the incident ion dose increased over 12×1017 ions/cm2. The elemental depth profile and surface roughness were obtained with X-ray photoelectron spectroscopy (XPS) and surface roughness tester, respectively.
Authors: Yong Tian Wang, Lu Lu Tao, Jia Wei Mo
Abstract: A 1mm thick Al-based composite coating was fabricated on the TC4 Ti-based substrate by using the amorphous powder and the pulse laser cladding technology. The microstructure, phase composition, hardness and friction of the coating were characterized by SEM, DSC, XRD and frictional wear tester, respectively. The results showed that the coating was composed of the micron-sized crystal phases and small amounts of amorphous matrix; the coating has the dense structure and metallurgically bonds with the substrate. The microhardness of the coating was up to 500-600 HV0.2, which was about two times of that of the TC4 Ti-based substrate. The friction coefficient of the coating was lower than that of the TC4 alloy, which improved the friction and wear properties of the TC4 substrate obviously.
Authors: G.V. Kalinnikov, R.A. Andrievski, V.K. Egorov
Abstract: Combined amorphous and nanocrystalline films attract an attention due to possibility to improve toughness, wear resistance and other properties which are important in nanomaterials and processes in energy systems. One of the known film fabrication methods is the magnetron sputtering deposition in the presence of an additional external magnetic field with inductions of up to 0.3 T as it was demonstrated by an example of the B4C-TiB2 system. The induction effects on the amorphous films hardness, growth rate and nanocrystallization process were investigated and discussed. The deposition under an additional external magnetic field with induction more than 0.2 T leads to the of nc-inclusions formation as was determined by X-ray diffraction, microdiffraction and high resolution transmission electron microscopy methods. The target and film compositions were determined by energy disperse spectroscopy and Rutherford backscattering spectroscopy. Compared to the target composition, some enrichment by nonmetallic elements (carbon and boron) was fixed in films.
Authors: Stéphane Godin, Denis Thibault, Jean Benoît Lévesque
Abstract: CA6NM and UNS S41500 martensitic stainless steels are widely used for manufacturing and repair of hydraulic turbine runners. They offer good mechanical properties and superior cavitation resistance when compared to mild steels. They are also relatively easy to weld. However, when welded homogeneously, they require a post-weld heat treatment (PWHT) in order to temper the as-welded martensite. This PWHT is also beneficial for residual stresses reduction as it effectively lowers the stress peaks. To avoid this PWHT, austenitic filler metals are often used for repair. But omitting PWHT inevitably leaves weld-induced residual stresses in the assembly. In order to better understand the impact of the weld filler metal choice on the importance of residual stress, an experimental study has been conducted on three different filler alloys. The chosen alloys were: • 410NiMo, a martensitic grade having the same composition as the base metal (13%Cr-4%Ni-0.5%Mo) ; • 309L, an austenitic grade widely used for repair (24%Cr-13%Ni) ; • A proprietary low transformation temperature (LTT) martensitic grade (13%Cr-6%Ni). This paper compares residual stresses in the as-welded condition on welds of UNS S41500 (13%Cr-4%Ni) made using these filler metals. Residual stresses were measured using the contour method. Microstructural analysis was performed to identify the phases in the weld and the heat-affected zones (HAZ). Microhardness maps were done to see the hardness distribution of each weldment.
Authors: De Juan Xie, Zong De Liu, Wei Qiang Hu, Yong Tian Wang
Abstract: Fe-based amorphous composite coatings were deposited on the surface of ASTM-1020 steel plate by different technologies: arc spraying, laser remelting, TIG remelting (with and without water cooling). The microstructure, phase structure and micro-hardness were characterized by using a combination of SEM, XRD and Vickers hardness tester. It shows that the coating prepared by arc spraying presents typical lamellar structure and poor adherence to the substrate. After the remelting treatment, the coating quality is significantly improved by decreasing structure defects such as cracks and pores; the interface shows the metallurgical bonding. The dendritic crystals could be obtained within all the remelted coatings with different appearances. The microstructures of TIG remelted coatings show much more regular and have obvious orientation, which cannot be seen in laser remelted coating. However, the average grain size of the laser remelted coating is much smaller than that of TIG remelted coatings. The micro-hardness values of all of the deposited coatings are much higher than that of the substrate, and the coating prepared by laser remelting shows the highest hardness.
Authors: Bojan Podgornik, Vojteh Leskovšek, Miha Kovačič, Joze Vižintin
Abstract: Plasma nitriding is a thermo-chemical process of high importance for engineering components, which through generation of near-surface compressive residual stresses significantly improves wear and fatigue resistance. A precise knowledge of the level and distribution of residual stresses that exist in surface engineered components is necessary for accurate prediction of a component’s fatigue resistance. However, measurement of residual stress is not always possible, especially in the case of industrial tools and dies. Therefore, other methods for residual stress evaluation and prediction are required by industry. Results of this investigation show that residual stress level and depth in plasma nitrided tool steel increase by nitriding time and temperature. On the other hand, experimental data show that residual steel distribution in plasma nitrided tool steels can be determined on the basis of microhardness depth distribution.
Authors: Ján Viňáš, Milan Ábel
Abstract: The paper presents results of quality analysis of the welded joints realized by CO2 laser (AF8P) using automotive body sheets and sheets for car chassis. There were used double-sided galvanized steel sheets of different grades and thicknesses. Welded joints were evaluated visually and then carrying capacity of the joints was established using tensile test. Welded joints were tested by following destructive tests: microhardness, macro and microstructure of the joints on metallographic sections using light microscopy. Results showed that the welding parameters were chosen appropriately.
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