A. Coban

Laser melting of plasma nitrided Ti6A14V alloy

Abstract A laser surface modification technique can be used as a part of a dublex treatment process to improve the surface properties of Ti6A14V alloy. The present study is conducted to investigate the surface properties of the Ti6A14V alloy due to laser melting prior to a plasma nitriding process. Consequently, nitriding is carried out to obtain the depth of the nitride zone of 30 μm. A CO 2 laser with 1.6 kW output power was used to melt the nitride layers. The wear properties of the plasma nitrided and nitrided/melted surfaces were investigated using pin-on-disc equipment while the friction coefficient was determined using a ball-on-disc machine. The nitride depth profile was measured using a nuclear analysis reaction and elemental distribution in the melted zones was investigated using μ-PIXE. Scanning electron microscopy and optical microscopy were carried out to analyze the microstructures developed before and after the laser melting process. In addition, heating and cooling rates were predicted through the electron-kinetic theory approach.

Introduction into the electron beam welding of austenitic 321-type stainless steel

Abstract Electron beam welding has great potential in the welding of engineering materials, since very narrow and deep penetration is possible with this process. Austenitic stainless steels are prone to inter-granular corrosion when subjected to sensitizing heat treatments between 723 and 1073 K, due to the formation of a titanium-depleted zone adjacent to a titanium-rich zone. However, during the electron beam welding of this material, the heat affected zone extends only to a narrow region across the weld pool, thus resulting in a lesser degree of defects in the weld zone. The present study is conducted to investigate the mechanical and metallurgical properties of electron beam welded austenitic 321 stainless steel. Consequently, microhardness tests across the heat-affected zone and tensile and impact testing of the resulting welds were carried out, with SEM and micro-particle induced X-ray emission (μ-PIXE) being carried out to study the microstructures and element distribution in the weld zone. In addition, analysis of the first- and second-law of thermodynamics of the welding process was carried out. It was found that the heat-affected zone increased as the workpiece thickness increased and that dendritic transverse microcracks were present at the boundary of the molten and solid regions.

Effect of Oxygen in Laser Cutting Process

Abstract Laser cutting has become an acceptable process in automated sheet metal industry. Efficiency and quality can be maintained with laser cutting. However, oxygen assisted cutting may influence the metallurgical structure of the cut edges. Consequently, in the present study, oxygen diffusion into solid substrate in the vicinity of the cut edge is considered together with the metallurgical changes at the cut surface. To achieve this, an experiment is designed and conducted to cut stainless steel workpiece with a CO2 laser beam at different oxygen pressures. To determine the elemental distribution in the vicinity of the cut edges, Micro-Particle Induced x-Ray Emission (μ-PIXE), Nuclear Reaction Analysis (μ-NRA) and EDS are carried out. It is found that no oxygen peak is evident at the cut edge and Cr, Al and Si are enriched locally.

Investigation into the properties of friction-welded aluminium bars

Abstract The replacement of copper by aliminium is inevitable for certain application in the electrical industry due to economic reasons. Whilst in the majority of cases, aluminium can be joined only by adhesive bonding, mechanical fastening and solid-phase welding techniques. Friction welding offers an alternative welding process for the joining the aluminium bars. Frinction welding is well known for its ability to weld aluminium to many metals and consequently is being considered seriously. The present study examines the friction welding of aluminium bars. Three welding parameters including welding time, speed of rotation and applied pressure are considered. To carry out a statistical analysis (factorial analysis) determining the affecting parameters on the mechanical properties of the resulting welds, each factor is considered at three levels. Metallurigical investigation is carried out using SEM and optical microscopy.

Difference between bulk and thin film densities of metal oxide and fluoride films studied by NRA depth profiling techniques

Abstract Nuclear reaction analysis techniques have been used to study the difference between bulk and thin film densities of different dielectric (WO3, MgF2, NdF3, LaF3 and ThF4) thin films. Thicknesses of the films were measured by optical methods. The 18 O ( p , α ) 15 N reaction was used at 730 keV to profile WO3 prepared with different thicknesses on a tantalum backing by thermal evaporation of natural WO3. We have also successfully tested the 18 O ( p , α ) 15 N reaction at the 629 keV (Γ=2.1 keV) resonance for the same purpose. Excitation function measurements of the reaction was performed around the resonant energy at a detection angle of 150°. In order to obtain the oxygen profiles of the thin films non-resonant part of the excitation function was deconvoluted using the known cross-section data of the reaction. Also, we studied different films of MgF2, NdF3, LaF3 and ThF4 using the 483.85 keV resonance in the 19 F ( p , αγ ) 16 O reaction.

Hydrogen embrittlement of Ti-6Al-4V alloy with surface modification by TiN coating

Ti-6Al-4V alloy is widely used in industry due to its excellent properties. However, hydrogen embrittlement may affect the mechanical properties of the alloy if the preventive precautions are not taken into account. Moreover, TiN coating of the substrate may reduce the diffusion rate of hydrogen in corrosive environments. Consequently, the present study is conducted to investigate the hydrogen diffusion into Ti-6Al-4V alloy when subjected to TiN coating. To achieve this physical vapor deposition (PVD) TiN coating of the alloy is realized and electrochemical testing of both workpieces, one coated and the other untreated, is carried out. This provided hydrogen diffusion into both workpieces, which in turn provides the comparison basis for the effect of TiN coating on the hydrogen embrittlement process. To measure the relative hydrogen concentration, the elastic recoil detection analysis (ERDA) technique is used while elemental analysis of the workpiece surfaces after the electrochemical treatment is carried out using the EDS technique. SEM microphotography is conducted to examine the hydrogen embrittlement in the vicinity of the substrate surface. The study is extended to include tensile testing of both TiN-coated and untreated workpieces before and after the electrochemical treatment. It is found that hydrogen diffusion reduces considerably for TiN-coated workpieces and local pitting occurs, which in turn initiates the hydrogen diffusion into the substrate. Tensile strength is slightly affected due to hydrogen embrittlement.

Investigation into some tribological properties of plasma nitrided hot-worked tool steel AISIH11

Interest in the tribological properties of plasma nitriding has increased substantially over the past years because plasma nitriding provides a high nitride depth and improved hard facing. The present study examines the tribological properties of AISI Hll plasma nitrided, hot- worked steel. Different nitriding temperatures and durations were considered. Characterization of the composite structures was investigated with wear tests, x-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and microhardness tests. The depth profile of the nitrided zone was measured using the nuclear reaction analysis (NRA) technique. Plasma nitriding affected the microhardness, wear properties, and morphology considerably. Increase in process temperature increased the nitride zone depth.

Investigation into nitrided spur gears

The cold forging method has been widely used in industry to produce machine parts. In general, gears are produced by shaping or hobbing. One of the shaping techniques is precision forging, which has several advantages over hobbing. In the present study, cold forging of spur gears from Ti-6A1-4V material is introduced. To improve the surface properties of the resulting gears, plasma nitriding was carried out. Nuclear reaction analysis was carried out to obtain the nitrogen concentration, while the micro-PIXE technique was used to determine the elemental distribution in the matrix after forging and nitriding processes. Scanning electron microscopy and x-ray powder diffraction were used to investigate the metallurgical changes and formation of nitride components in the surface region. Microhardness and friction tests were carried out to measure the hardness depth profile and friction coefficient at the surface. Finally, scoring failure tests were conducted to determine the rotational speed at which the gears failed. Three distinct regions were obtained in the nitride region, and at the initial stages of the scoring tests, failure in surface roughness was observed in the vicinity of the tip of the gear tooth. This occurred at a particular rotational speed and work input.

Analysis of a plasma nitrided Ti-6Al-4V spur gear surface

Abstract The unworn and worn surface of a cold forged and plasma nitrided Ti-6Al-4V gear was analyzed for the distribution of elements. Titanium, aluminum and vanadium distributions were mapped using the micro-PIXE technique, while nitrogen concentration and depth profiles were carried out in the surface region by NRA resonance profiling, and also micro-NRA techniques using the nuclear reaction 15N(p,αγ)12C. The nitrogen layer thickness was determined as about 17 μm below the surface, and the concentration at the surface reached the value of up to 16 mass%. Due to plasma nitriding process aluminum and vanadium were found depleted in the first few micrometers from the surface. It was evident that local agglomeration occurred for both elements in the surface layer. This was probably caused by the residual stresses developed during the forging process.

Analysis of hydrogen in corrosion product films on molybdenum and niobium using ERDA technique

Elastic Recoil Detection Analysis (ERDA) technique with 1H(α,α)1H forward scattering was used at 3.0 MeV to analyze hydrogen in corrosion product films formed on molybdenum and niobium surfaces at selected potentials of the anodic and cathodic potentiodynamic scan. Hydrogen in the corrosion film on molybdenum was found to be linearly increasing with the polarizing potential. On the other hand, niobium film is found to be less permeable to hydrogen in the active region compared to the passive region of the voltammogram.