Papers by Keyword: Gas Nitriding

Abstract: In the scope of this study, quenched and tempered H13 steel samples were subjected to conventional (CN) and low temperature (LTN) gas nitriding in a fluidized bed reactor. Structural examinations revealed that surfaces of the CN sample were covered with about 1-2 µm thick compound layer (CL) with an underlying ~30 µm thick nitrogen diffusion zone (NDZ), while outer surface of the LTN sample consisted of ~25 µm thick NDZ. The surface hardness values were measured as 1320 HV_0.1 for LTN sample and 1220 HV_0.1 for CN sample. Under impact sliding conditions, wear mechanisms of the CN and LTN samples were determined as “oxidation + fatigue” at RT and “plastic deformation” at 600 °C. As a general trend CN sample exhibited better impact sliding wear resistance compared to LTN sample both at RT and 600 °C.

Abstract: Overview of Gas nitriding on the surface of industrial pure iron and laser gas nitriding, research under different nitriding process, the phase, organization and mechanical properties of the nitride layer that is the difference. Plasma sprayed titanium on industrial pure iron surface, the laser nitriding experiments were carried out on the titanium surface. The formation of iron and nitrogen compounds is induced by the combination of titanium nitride. The difference between gas nitriding and laser nitriding is analyzed. The results show that: (1) after gas nitriding, the nitrides formed on the surface of pure iron are mainly ε-Fe_2-3N and γ′-Fe₄N, the surface hardness is 158 HV, and the increase is 32%. (2) in the 500 W laser power, laser nitriding formed on the surface of Titanium metal layer of pure iron, but not the formation of iron and nitrogen compound, the surface hardness of 168 HV, increased by 46%. (3) under the condition of 500 W laser power, the industrial pure iron was nitrided by laser, without the formation of iron and nitrogen compounds, but the surface hardness of the sample was increased by 20%.

Abstract: The Ti-6Al-4V alloy was nitrided at 950 °C for 8 h by heating under atmospheric nitrogen in order to improve its surface hardness and oxidation resistance. Nitrogen diffused into the Ti6Al4V alloy, and formed ~40 μm-thick coating consisting of TiN as the major phase and Ti₂N as the minor one. Nitriding increased the surface microhardness through the strengthening effect of interstitial nitrogen and the formation of nitrides. Oxidation at 700 °C for 10 h formed a superficial TiO₂ layer on the coating.

Abstract: A composite surface layer was fabricated on a high-vanadium alloy steel (HVAS) plate by means of a surface gas nitriding at 550°C for 70h. The microstructural charaterization and phase analysis of resultant nitride layers were performed using optical, scanning electron microscopy, electron probe microanalyzer, X-ray diffraction methods and hardness measurements. The results of the investigation showed that a composite layer consisting of ε-Fe_2–3N and γ'-Fe₄N phases is feasible on the surface of HVAS. Vickers hardness test indicate that the hardness value of the nitrided sample is about 1100 HV at the top surface, and decreases gradually to about 700 HV in the matrix. The depth of hardened layer after surface gas nitriding was about 200 μm.

Abstract: Gas atomized Ti-6Al-4V (Ti64) alloy powder was used to prepare distinct designed geometries with different properties by selective laser melting (SLM). Several heat treatments were investigated to find suitable processing parameters to strengthen (specially to harden) these parts for different applications. The results showed significant differences between tabulated results for heat treated billet Ti64 and SLM produced Ti64 parts, while certain mechanical properties of SLM Ti64 parts could be improved by different heat treatments using different processing parameters. Most heat treatments performed followed the trends of a reduction in tensile strength while improving ductility compared with untreated SLM Ti64 parts.Gas nitriding [GN] (diffusion-based thermo-chemical treatment) has been combined with a selected heat treatment for interstitial hardening. Heat treatment was performed below β-transus temperature using minimum flow of nitrogen gas with a controlled low pressure. The surface of the SLM produced Ti64 parts after gas nitriding showed TiN and Ti₂N phases (“compound layer”, XRD analysis) and α (N) – Ti diffusion zones as well as high values of micro-hardness as compared to untreated SLM produced Ti64 parts. The microhardness profiles on cross section of the gas nitrided SLM produced samples gave information about the i) microhardness behaviour of the material, and ii) thickness of the nitrided layer, which was investigated using energy dispersive spectroscopy (EDS) and x-ray elemental analysis. Tensile properties of the gas nitrided Ti64 bars produced by SLM under different conditions were also reported.

Abstract: Nitriding treatment is well known as one of the corrosion protection methods for steels as well as a way to prevent wear and fatigue. Initially, salt bath nitrocarburizing was popular, but recently, gas nitriding, gas nitrocarburizing, plasma nitriding and so on have come to be used more often because of their superior nitriding ability. In the case of nitriding, only nitrogen (N) diffuses into the steel, but in the case of nitrocarburizing, both nitrogen and carbon (C) diffuse into the steel. General speaking, nitriding includes all the treatments mentioned above. The corrosion behavior of nitride carbon steels has been understood mainly by salt bath or gas nitrocarburizing treatments^1)-4).However, recently, nitriding is mainly applied to parts for things such as automobiles which need protection from wear and fatigue, and is seldom used for parts which need corrosion resistance. The present paper is to remind researchers again that nitrided steels show good corrosion resistance.Therefore, the comparison of various thicknesses of nitride layers as well as the comparison between nitride layers on steel has been carried out in this examination, using the salt spray corrosion test method. The effect of oxidation treatment after nitriding was also investigated.

Abstract: Nitriding is the most common surface engineering technique that is being used in Titanium alloys for improving their surface properties, viz hardness, wear resistance, etc. Ti6Al4V (Grade 5) Titanium Alloy is a super alloy that exhibits excellent mechanical strength; it is highly resistance to creep at very high temperatures which maintains good surface stability. It is resistant to corrosion and oxidation. The main objective of this review paper is to study the recent research works carried on Nitriding of Ti6Al4V alloy by using, viz gas Nitriding and laser Nitriding. This process is used in the surface hardening of machine parts such as aircraft engine parts, crank pins, valve seats, gears, bush, aero engine cylinders, aero crank shafts. Gas Nitriding is a diffusional technique in which the nitrogen atoms are diffused into the surface of the metal to obtain hard surface. By Laser Nitriding is a diffusional technique by which the surface properties of the titanium alloy is enhanced. Laser nitriding process comprises of various stages, viz, transport of heat, melting effect, diffusion and convection effect. By Nitriding technique the surface hardness of super alloys like Titanium Alloy Ti6Al4V Grade 5 can be increased by increasing the hardness on the surface there by its scope of application is widened. In this paper a literature survey is carried out and the recent research works on surface engineering of Ti6Al4V alloy using gas and laser Nitriding technique is summarized.

Abstract: The present work deals with the evaluation of the residual-stress profile in expanded-austenite by successive removal steps using GI-XRD. Preliminary results indicate stresses of several GPa's from 111 and 200 diffraction lines. These stresses appear largest for the 200 reflection. The strain-free lattice parameter decayed smoothly with depth, while for the compressive stress a maximum value is observed at some depth below the surface. Additionally a good agreement was found between the nitrogen profile determined with GDOES analysis and the strain-free lattice parameter from XRD.

Abstract: In this paper the emphasis is focused upon nitriding effect on corrosion fatigue strength of Cr-Mo low alloy steel in 1% HCl aqueous solution.Corrosion fatigue strength enhancement of Cr-Mo low alloy steel by nitriding is discussed on the basis of the corrosion fatigue testing results on gas and ion nitrided Cr-Mo low alloy steel plate specimen with 3.5mm thickness in 1%HCl aqueous solution. It can be concluded that residual compressive stress distributed on the nitrided specimen surface caused improvement of corrosion fatigue strength of Cr-Mo low alloy steel.

Abstract: The RERTR Program (Reduced Enrichment in Research and Test Reactors) is an attempt to utilize uranium fuel enriched below 20% for nuclear research reactors. Since the program was launched by the United States in 1978, the International Atomic Energy Agency (IAEA) has recommended that UxSiy alloys, particularly U₃Si₂ and U₃Si compounds, be used to fuel nuclear research reactors with uranium loading rate up to 4.8 gU/cm³. Unfortunately, there are difficulties in reprocessing U₃Si₂ and U₃Si compounds due to the Si content. To overcome this problem, the IAEA initiated international cooperation to find the best solution in the development of new nuclear fuels to substitute the UxSiy alloys. In order to synthesize nuclear fuel containing high loading of uranium, research in developing uranium nitride (UN) from uranium metal has been conducted by reacting the massive uranium metal with hydrogen gas at a temperature of 573 K followed by dehydriding at a temperature of 773 K under vacuum pressure and nitriding at a temperature of 1073 K by introducing nitrogen gas in the reaction chamber. The X-ray diffraction analysis results showed that the hydriding process caused the uranium metal to turn into a stable compound, UH₃, which was identified by the changes of the massive shapes into fine metal powders. Dehydriding process at a temperature of 773 K caused the UH₃ compound to decompose into U metal powders, and when the metal powders were reacted with N₂ gas at 1073 K a stable phase identified as UN was formed. The results showed that it is possible to produce UN powders by hydriding, dehydriding, and nitriding process, although special handling of UH₃ and UN powders is required due to their pyrophoric nature.