Surface Alloying Process Research Articles

Research on the Carbides of Its Alloying Layer Conducted by W-Mo-Y Surface Alloying and Carburizing Process

Q235 steel was processed by solid carburizing and quenching after conducted by W-Mo-Y double glow-discharge plasma surface alloying process. Finally carbon contents, the morphologies and phases of the samples' surface were analyzed. The results show as follows: Carbon contents of the samples' surface are 1.28 wt%, 1.36 wt%, 1.51 wt% respectively after W-Mo-Y alloying layer (also called co-penetrated layer) was processed by solid carburizing at 960 °C, 980 °C, 1020 °C respectively; The amount of the carbides in W-Mo-Y alloying layer is obviously more than that of the carbides in W-Mo alloying layer; The granular carbides distribute dispersively and uniformly in alloying layer, and the sizes of carbide particle are less than 1 μm; There is no eutectic carbide at the grain boundaries; With temperatures of carburizing and quenching process rising, the carbides increases in number; After W-Mo-Y alloying layer was carburized and quenched at 1020 °C, the phases of alloying layer are Fe2C, W2C, Fe2MoC, MoC, Fe3C, Mo2C and Y2C3; and the types of their carbides are M3C, M2C, and MC, which are different from the types of W-Mo carbides in general metallurgy high-speed steel (HSS). It can be seen from the available, the morphologies, the sizes and the amount of surface HSS's carbides can be adjusted by heat treatment.

Analysis of Unit and Binary Diffusion in Glow Plasma Surface Alloying Process

Q195 steel was conducted by plasma chromizing and Cr-Ni surface alloying process to research the relationship between unit diffusion and binary diffusion. After studying the thickness, composition, phase component of the layer and diffusion coefficients of alloying elements, results showed that (1) the thickness of chromizing layer was 150μm; the surface phase component was Fe-Cr solid solution; the surface chromium contents was 21.4%. The thickness of Cr-Ni co-diffusion layer was 40μm; the surface phase component was Fe-Cr-Ni solid solution; the surface contents were: Cr 16.14%, Ni 48.16%. The alloying elements distributed in downward gradient from the outside to the inside. (2) Compared with plain surface alloying technique, using plasma surface alloying technique can get higher diffusing speed and shorten production cycle time. (3) The diffusion coefficients decreased as the diffusion distance increased. (4)Compared with chromizing, Cr-Ni co-diffusion increased the utilization ratio of alloying elements but decreased the diffusion speed of alloying elements, thus the surface alloying content increased and the thickness of alloying layer decreased.

Effects of C, N-codoped on the corrosion resistance of TiO2 films prepared by plasma surface alloying and thermal oxidation duplex process

C, N-codoped TiO2 films have been deposited onto stainless steel substrates using plasma surface alloying and thermal oxidation duplex process. Composition analysis shows that the films shield the substrates entirely. The TiO2 films are anatase in structure as characterized by X-ray diffraction. The electrochemical measurements show that the equilibrium corrosion potential positively shifts from −0.275 eV for bare stainless steel to −0.267 eV for C, N-codoped TiO2 coated stainless steel, and the corrosion current density decreases from 1.3×10−5 A/cm2 to 4.1×10−6 A/cm2. The corrosion resistance obtained by electrochemistry noise also reveals that the C, N-codoped TiO2 films provide good protection for stainless steel against corrosion in stimulated body fluid. The above results indicate that C, N-codoped TiO2 films deposited by plasma surface alloying and thermal oxidation duplex process are effective in protecting stainless steel from corrosion.

Study on Tribological Performance of the TiNi Modified Layer on the Surface of the Ti6Al4V Alloy

TiNi alloyed layer was prepared on surface of Ti6Al4V substrate by plasma surface alloying process. Micro-structure, composition distribution, phase structure and hardness distributing of TiNi modified layer were analyzed. Tribological performance of TiNi alloyed layer and Ti6Al4V substrate was observed by Pin-on-disc test. The results indicated that surface microhardness of TiNi alloyed layer was about 620HV. Coefficient of friction (CoF) and relative wear rate (RWR) of TiNi alloyed layer were lower than Ti6Al4V substrate, and wear resistance of TiNi alloyed layer was improved obviously. The wear mechanism of Ti6Al4V alloy is abrasion and adhesion wearing, while TiNi alloyed layer shows abrasion wearing.

Properties of TiN Coating Prepared on 3Cr2W8V by Electron Beam Surface Alloying Process

TiN coating was deposited on 3Cr2W8V alloy by PVD and then processed with electron beam surface alloying process. The microstructure, microhardness, friction coefficient, amount of wear and corrosion resistance of electron beam treated specimens were investigated. It is shown that the electron beam treated specimens can improve the properties of material. The coating has an average microhardness of approximately HV800, the friction coefficient of electron beam irradiation treated specimens is considerably lower than that of TiN coating. When the electron beam irradiate times is appropriate, the roughness of surface will much lower, and it will achieve polishing effects. The corrosion behavior of the composite coating in 3.5% Nacl solution at room temperature was also determined using a potentiont state system. In comparion with the corrosion potential for 3Cr2W8V alloy, the corrosion potentials of TiN coating and electron beam treated specimen are increased respectively. The electron beam treated specimen has the lowest corrosion current density as well as the highest corrosion potential showing an improved corrosion resistance compared with 3Cr2W8V alloy.

Characterization of the discharge in array needle cathodes and applications

In this paper, a new direct current (DC) plasma source for surface alloying using array-needle-cathode has been designed and manufactured. The array-needle-cathode is used to produce a stable abnormal glow discharge plasma in a rectangular chamber. During the surface alloying process, it is noticed that the discharge modes severely influenced the plasma parameters including electron density (Ne) and electron temperature (Te). The Te obtained by optical emission spectrometry (OES) through the comparison of the relative intensity of N in 3919Å and 3995Å is between 1.44eV and 5.40eV. The distribution and fluctuation of Te in the two-dimensional planar are revealed by analysis of digital camera images. It is concluded that the discharge by the array- needle-cathode is a kind of new plasma source which can generate stable plasma with a high electron temperature applicable for surface alloying. Lastly, with this array-needle-cathode plasma source (ANCPS), W-Mo-N alloyed layer on Ti alloy is explored in this paper.

Computational modelling of transport phenomena in high energy materials processing application: large eddy simulation and parallelisation

A comprehensive three-dimensional numerical model is presented in order to address the coupled turbulent momentum, heat and species transport during molten metal-pool convection in association with continuous evolution of solid-liquid interface typically encountered in high energy materials processing applications. The turbulent aspect is handled by a large eddy simulation (LES) model and the phase changing phenomena is taken care of by a modified enthalpy-porosity technique. The proposed finite volume based LES model is subsequently parallelised for effective computational economy. To demonstrate the effectiveness of the present model, a systematic analysis is subsequently carried out to simulate a typical high power laser surface alloying process, where the effects of turbulent transport can actually be realised.

Microstructure and Properties of Mold Steel 3Cr2W8V by Electron Beam Surface Alloying

Ti coating was deposited on mold steel 3Cr2W8V by PVD and then processed with electron beam surface alloying process. The microstructure, surface roughness and microhardness of electron beam surface alloying treated specimens were investigated by using metallurgical microscope, SEM , XRD, micro hardness tester and roughness tester. It is shown that the electron beam surface alloying treated specimens have a rapidly solidified microstructure consisting of the uniformly distributed TiC phases and fine VCrFe8 intermetallic phases.The coating has a strong metallurgical boning with substrate, and the coating has high hardness, excellent wear resistance. The coating layer has an average microhardness of approximately HV600, 35% higher than the substrate’s. So it is used widely. Furthermore the need for further research is discussed as well.

Effect of different alloyed layers on the high temperature oxidation behavior of newly developed Ti 2AlNb-based alloys

The application of titanium aluminide orthorhombic alloys (O-phase alloys) as potential materials in aircraft and jet engines was limited by their poor oxidation resistance at high temperature. The Ti 2AlNb-based alloys were chromised (Cr), chromium–tungstened (Cr–W) and nickel–chromised (Ni–Cr) by the double glow plasma surface alloying process to improve their high temperature oxidation resistance. The discontinuous oxidative behavior of Cr, Cr–W and Ni–Cr alloyed layers on Ti 2AlNb-based alloy at 1093 K was explored in this study. After exposing at 1093 K, the TiO 2 layer was formed on the bare alloy and accompanied by the occurrence of crack, which promoted oxidation rate. The oxidation behavior of Ti 2AlNb-based alloys was improved by surface alloying due to the formation of protective Al 2O 3 scale or continuous and dense NiCr 2O 4 film. The Ni–Cr alloyed layer presented the best high-temperature oxidation resistance among three alloyed layers.

The effect of hydrogen shielding gas on microstructure and abrasive wear behavior in the surface modification process using the tungsten inert gas method

In this study, SAE 1020 steel surfaces were separately alloyed with preplaced high-carbon ferro-chromium (FeCr), ferro-molybdenum (FeMo), and ferro-titanium (FeTi) powders by using a tungsten inert gas (TIG) heat source. By using two different types of shielding gas compositions during the alloying process, the study investigated the effects of modified shielding gas composition on the microstructure, hardness, and abrasive wear resistance of specimens. It was observed that with modifications in shielding gas composition, the microstructure and volume hardness of the specimens changed and no cracks and voids were formed in the interface area. The X-ray examinations of the specimens identified Fe, FeTi, and FeMo phases in their microstructure as the first phase, and Cr7C3, Fe3C, Fe7C3, and TiC phases as the second phase. As a result, it was concluded that changes in shielding gas composition in surface alloying process significantly affect specimens’ microstructure and mechanical properties.

Production of nitrogen and carbon S phases in austenitic stainless steels by hybrid plasma surface alloying

The discovery of the S phase phenomenon during low temperature nitriding of austenitic stainless steels by Tom Bell and others in the 1980s has stimulated significant international interest not only in the research but also in the industrial community. This has led to the intensive research on the S phase technology during the past two decades and the development and industrial acceptance of several important low temperature techniques to enhance the tribological and biological properties of austenitic stainless steels and related materials without compromising their corrosion resistance. These include low temperature nitriding by various methods, low temperature carburising and the hybrid surface alloying process combining nitriding and carburising. The present paper discusses the recent development in the hybrid plasma surface alloying process, which involves incorporating both nitrogen and carbon in the surface region of austenitic stainless steels to form a dual layer structure comprising a nitrogen S phase layer on top of a carbon S phase layer. This paper is presented to highlight the seminal contribution of Professor Tom Bell to the S phase technology.

Corrosion-Wear Behavior of TiO<sub>2</sub> Films in Hanks’ Solution

TiO2 films were fabricated on stainless steel (SS) substrate by plasma surface alloying and thermal oxidation duplex process. Composition and microstructure of the films were characterized using glow discharge spectrometer (GDOES), X-ray photoelectron spectroscopy (XPS) and XRD. Results reveal that the TiO2 films are dense, homogeneous and existed in a complete anatase structure. Both Ti and O elements show gradient distribution in the films. The wear behavior of TiO2 films in Hanks’ solution indicates that the films display much better wear resistance and antifriction performance than that of SS substrate. Electrochemistry noise tests indicate that the TiO2 films effectively retard the local pitting and crevice corrosion of the SS substrate.

Process monitoring of powder pre-paste laser surface alloying

Instead of the continuous powder delivery method using a powder feeder for thick layer laser cladding, pre-pasting of the alloying powder on the substrate is a widely used method to supply the coating powders into the melt pool for LSA. A method to monitor the process of laser surface alloying based on the infrared emission from the melt pool using infrared photodiodes was developed. The technique is solely aimed at the process of laser surface alloying using pre-paste metal powder on the substrate surface prior to laser melting. This monitoring technique is able to distinguish the existence or the absence of the pre-paste powder and the consistency of the laser surface alloying process. The technique is of low cost and is simple to implement into the process.

Surface Alloying of Mg Alloys After Surface Nanocrystallization

Surface nanocrystallization using a surface mechanical attrition treatment effectively activates the surface of magnesium alloys due to the increase in grain boundary diffusion channels. As a result, the temperature of subsequent surface alloying treatment of pure Mg and AZ91 alloy can be reduced from 430 degrees C to 380 degrees C. Thus, it is possible to combine the surface alloying process with the solution treatment for this type of alloy. After surface alloying, the hardness of the alloyed layer is 3 to 4 times higher than that of the substrate and this may significantly improve the wear resistance of magnesium alloys.

Effect of scanning speed, nozzle stand-off distance and beam scan-off distance on coating properties of laser surface alloyed 13Cr-4Ni steel

The present work describes an investigation of the effect of 3 different parameters of laser surface alloying—i.e., laser scanning speed (LSS), nozzle stand-off distance (NSOD) and laser beam scan-off distance (LBSOD) on coating height, depth and width. Nickel-based Colmonoy 88 alloy powder has been deposited on 13Cr-4Ni steel by single-step process of laser surface alloying. Laser power and powder feed rate were maintained at 3kW and 25 g/min, respectively. L8 orthogonal array has been designed to study these 3 parameters at 2 levels each. The results of single pass with extent of dilution, surface hardness and microstructures produced by different conditions are presented and discussed. For a specified NSOD and LBSOD, there was a decrease in coating height and depth with increase in LSS. Coating height and depth were not affected much by increase in NSOD. From the present investigation, optimized parameters were identified for enhanced hardness, minimum dilution and desired coating height and coating depth.

Study on Temperature Distribution in Double Glow Discharge Zone

This paper deals with the temperature measuring of the glow discharge zone in double glow plasma surface alloying process. CCD technique was employed to get the temperature distribution profile. The results show that CCD method is a simple and effective non-contact temperature measuring technique, applicable in fields of low temperature and high temperature plasma processes.

Multiple Needle Cathodes Plasma Surface Alloying of Ti6Al4V with W-Mo-C-N

A multiple-needle-cathode plasma surface alloying process has been developed for improving the properties of surface hardness, wear resistance and corrosion resistance of Ti6Al4V. The process is carried out at temperatures below 800 °C and facilitates the simultaneous introduction of W, Mo,nitrogen and carbon into the surfaces of Ti6Al4V forming gradient alloying layer structure with an extremely high hardness. The process is performed at working pressure of 30Pa-80Pa with 9-needle-cathode of W80Mo20 alloy rods array and a high pure graphite plate cathode as target electrode. A maximum microhardness is 4-6 times much harder than the substrate. The results show the presence of carbide and nitride ceramics phases contribute to high microhardness and wear resistance. The multiple-needle-cathode discharge plasma treatment is an effective method for improvement of the mechanical and tribological properties of titanium-base alloys by formation of graded diffusion hard surface layers. The present paper describes this novel process and properties characteristics.

Influence of processing conditions on structural characteristics of hybrid plasma surface alloyed austenitic stainless steel

A hybrid plasma surface alloying process has recently been developed for austenitic stainless steels to improve their surface hardness, wear resistance and corrosion resistance. The process is carried out in nitrogen and methane gas mixtures at temperatures below 450°C and facilitates the simultaneous incorporation of nitrogen and carbon into the surfaces of austenitic stainless steels, forming a dual layer structure with an extremely hard nitrogen-enriched layer on top of a hard carbon-enriched layer. The present paper discusses the influence of three most important processing parameters, i.e., gas composition, temperature and time, on the structural characteristics of the alloyed zones produced on AISI 321 stainless steel, in terms of layer morphology, growth kinetics and chromium compound precipitation. It was found that the development of the alloyed layers is diffusion-controlled, and under proper processing conditions, a precipitation-free dual-layer structure can be produced, with nitrogen and carbon dissolved in the relevant layer forming N-expanded austenite and C-expanded austenite respectively. Based on the experimental results, a threshold temperature–time curve has been established for the investigated austenitic stainless steel.

Ti6Al4V laser alloying process monitoring by using adaptive neural network controller

Since the surface alloying process has multi-input and multi-output, non-linear coupling and time varying dynamic characteristics, it is very difficult to establish an accurate process model for designing model-based controller. Hence an adaptive neural network controller is developed in this paper to tackle the variation and disturbance of the laser alloying control system. The proposed control strategy is based on a neural network structure combined with sliding-mode control scheme. An adaptive rule is derived based on the reaching condition of a specified sliding surface to on-line adjust the weights of radial basis functions neural network (RBFNN). It has on-line learning ability in response to the system's non-linear and time-varying behaviors. Two adaptive neural network controllers are designed for regulating the laser power control and traverse speed, respectively, to achieve the desired temperature distribution on the alloying surface. The control performance is evaluated based on numerical simulation results. Different disturbances are introduced into the system output variables to investigate the robustness of the proposed controller with respect to practical process variation.

Investigation of a TIG-Welded Layer Alloyed with Ferromanganese Powder on the Surface of a Copper Alloy

Abstract In this study, alloyed layers of 1.5-1.8 mm thickness were formed on the Cu based material surface using the Gas Tungsten Arc welding (GTAW) process. After the preliminary studies and sample preparation as groups I, II, and III, the surface alloying process was performed with 115 A, 125 A and 140 A current values, 6 g, 9 g and 12 g powder feed contents, and by determining voltage coefficients at 25 V and 28 V, respectively. Penetration of ferromanganese on the underlay was ensured using optimized coating parameters. In the ferromanganese layer different hardness values were determined according to the amount of powder fed. These hardness values were correlated to the thermal conductivity of Cu at the respective energy input. The impact resist of the coated specimens was increased. These toughness increments were attributed to newly formed structures in the microstructure with the effect of thermal conductivity and hardness of coated surface. Changes in powder feed time and powder feed rate and energy input were calculated from application parameters.