Volume 58, Issue 9

Micro-magnetic testing methods are qualified for non-destructive quantification of hardness, hardness depth and residual stresses. Among others they are applied for detection of grinding burn in gear wheels, but an application for wear condition monitoring has not yet been published. In this paper, results of initial research of determination of wear condition in gear wheels by application of micro-magnetic testing systems are presented. For comparison of different wear conditions, gears were loaded for increasing numbers of cycles in a test rig based on FVA information sheet 54/7 and DIN ISO 14635 part 1. Operating conditions were altered by usage of different lubricants. Afterwards, wear conditions were determined by conventional techniques, i. e., measuring change in profile and loss of material. Four measurement principles were evaluated for change in micro-magnetic properties determination, magnetic Barkhausen noise analysis, permeability and eddy-current measurements, as well as harmonic analysis of tangential field strength. A general suitability of micro-magnetic testing approach for characterization of wear condition of gear wheels could be demonstrated by comparison of micro-magnetic properties with common wear indicators. Micro-magnetic properties were not solely influenced by wear condition, as the selected oil, and hence the tribochemical conditions in contact also showed a significant effect on measured values. Therefore, further survey is required for direct correlation of micro-magnetic properties with (micro-)structural material changes.

The aim of this study is to investigate the effect of a monel/nickel interlayer electrode prepared with a thickness of 2 mm on the weldability properties of duplex stainless steel plates welded by means of plasma transfer arc welding. After welding, scanning electron microscopy, X-ray diffraction and energy dispersive spectrometry were carried out to determine the microstructural changes that occurred in the interface regions of the welds. Moreover, tensile strength, microhardness and fractography tests were conducted for assessing the mechanical properties of the welded specimens. The results of tests and examinations indicated that the tensile strength of welded parts with a nickel interlayer was higher than that of with and without a monel interlayer.

The deposition of Ti on steel substrates using a Cu interlayer was experimentally investigated using the tungsten inert gas technique with a mechanized feeding system. First, a Cu layer was deposited on the steel surface before the coating process for the production of the Ti layer. The resulting depositions exhibit a good penetration following the occurrence of two heat affected zones with a dense, compact and free-of-cracks microstructure. The investigations by scanning electron microscopy and by X-ray diffraction showed the formation of compounds in the Ti-Cu system and the absence of chemical combinations between Ti and Fe that can strongly affect the toughness characteristics of the deposited layer. The measurement of the cross-sectional hardness shows a significant increase in the surface compared to that of the substrate.

High alloy steels are widely used for high temperature and corrosion resistance applications in power plants, e. g., in chemical and petroleum industries. Mechanical properties of these alloys (e. g., hardness and tensile strength) can be altered by suitable heat treatment. This paper deals with failure investigations of a cast valve made of high alloy steel. The samples were taken from valve body and prepared by metallographic techniques. Microstructural defects causing cracking were investigated using light microscopy and scanning electron microscopy/energy dispersive X-ray spectrometry. Segregation areas at the grain boundaries in the microstructure of the material were observed. Casting was repeated by taking necessary measures during the production in order to eliminate these heterogeneous regions and then suitable heat treatment was applied to the part. The samples taken from the last part were also examined. As a result, a homogeneous microstructure was obtained and no macro or micro cracks were observed.

Diffusion welding is one of the exclusive welding methods that provides a perfect material interface after joining of different materials and results in high mechanical properties at high temperatures. In particular, this technique can be used for joining porcelain and metal that have distinctly different features. In this study, diffusion welding of copper to porcelain has been investigated. After the diffusion welding with different parameters, shear tests have been applied to the samples in order to investigate the weld properties and the changes in hardness in the weld region. In order to elucidate the changes in microstructure and composition in the weld region, SEM, EDX and XRD analyses were performed on the samples. As a result, the joining of copper and porcelain materials can successfully be performed by diffusion welding. Samples have the highest weld strength, if they are joined by diffusion welding at 900 °C for 60 min and at 4.5 MPa.

Being widely used in automotive, machinery, aviation and aerospace industry, solid-sate friction welding was applied in this study. AISI 420 martensitic stainless steel, being difficult to be joined by using fusion welding methods, was joined by friction welding. During the welding process, three rotational speeds (R) of 700, 1000 and 1300 rpm were used and other parameters such as friction pressure (Fp), friction time (Ft), upsetting pressure (Up) and upsetting duration (Ud) were kept constant. After the welding process, a torsion test was performed with these samples. The torsion angle (Ta) – torque (T) graphics of the samples were evaluated. Additionally, the fracture surface of the samples was examined by using SEM. As a result, it was observed that the AISI 420 steel was welded without problems by using friction welding. During the torsion tests, the samples fractured outside the welded joint zones. Thus, it was concluded that torsional strength of the welded joints was high.

In this study, commercially pure (99.5 wt.-%) copper alloy plates were brazed using an oxy-gas flame with four different brazing alloys in butt and lap joints, and the brazing capability, the microstructural and mechanical property changes were examined. The experimental results showed that L-CuZn39Sn brazing wire used in the butt joining caused porosity and an adverse effect on the microstructural and mechanical properties. However, in lap joining, it was observed that the mechanical properties of this material show identical characteristics compared to other brazing wires. In lap joining conducted using the L-CuNi10Zn42 alloyed brazing wires, a very good grain structure originated by diffusion was observed.

The Fe-B-Al alloy containing 0 to 10.0 wt.-% Al was melted in a vacuum induction furnace. Effects of the aluminum addition on the microstructure and properties of Fe-B-Al alloys were studied by means of optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), hardness testing and MMG-500 type pin-on-disk high temperature vacuum wear testing. The results showed that the as-casted microstructure of the aluminum-free Fe-B alloy consisted of α-Fe, Fe 2 (B,C), and Fe 23 (B,C) 6 type borocarbides. However, the as-casted microstructure of the Fe-B-Al alloy consists of a Fe 3 Al type intermetallic compound when the aluminum content is more than 6.0 wt.-%. Compared with the aluminum-free Fe-B alloy, parts of the borocarbide networks are broken, and the fracture tendency became more obvious with the increase of the aluminum content. Boron is mainly distributed over the borocarbide. Aluminum is mainly distributed over the matrix and Fe 3 Al type intermetallic compound. Compared with the aluminum-free Fe-B alloy, the addition of a small amount of aluminum reduces slightly the hardness. The hardness gradually increased with the further increasing of the aluminum content. The hardness reached 48.1 HRC when aluminum content was 10.0 wt.-%. The high temperature wear resistance of Fe-B-Al alloy gradually increased with the increase of the aluminum content. When the aluminum content reached 10.0 wt.-%, the high temperature wear resistance of the alloy was the best.

Three unused domestic fuel rods were investigated qualitatively and quantitatively by means of thermal neutron radiography. The neutron radiography tests were performed by the image plate method at Tehran research reactor in order to check the fuel properties. The pellets of these three fuel rods contained three different U-235 enrichments and different sizes that were filled into a zircalloy tube. In the qualitative investigations, the difference in size and enrichment between the pellets and the gaps between them were obviously recognized in the image of the fuel rods. In the quantitative investigations, data of the pellets compositions, their sizes (lengths and diameters) and the gaps between them were extracted from obtained images. It was found that the measured data and the manufacturer's specifications are in good agreement.

This paper presents the results of the application of carbon rovings as strain sensors for measuring the strain in concrete. In this work, three types of electrically conductive carbon roving with different characteristics were used. The possibility of using carbon rovings as a strain sensor is demonstrated via measurements in tensile and four point bending tests. The experimental setups and methods for measuring the electrical resistance of carbon roving in the roving and concrete are described. The results of the characterization of the electrical behavior as a function of strain of carbon rovings and concrete are presented and discussed. The obtained results indicate that the strain range of carbon rovings optimally corresponds to the strain range of concrete. This characteristic behavior makes the carbon rovings well suited for the use as strain sensors. A good correlation has been found between the electrical resistance-strain curve of the carbon roving and the measurements in the concrete.

The aim of this study is to explore wear behaviors of carbide tools with a multilayer TiCN + Al 2 O 3 + TiN coating on AISI-4340 and AISI-52100 hardened steel substrates generated by the medium temperature chemical vapor deposition (MTCVD) method in finish dry hard turning. Microscopic and microstructural wear aspects of multilayer-coated carbide tips were quantified at three cutting speeds using a constant feed rate of 0.027 mm × rev −1 and a constant cutting depth of 0.2 mm. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to investigate worn tool surfaces, wear products and wear mechanisms. Wear mechanisms observed involved abrasion, adhesion, plastic flow, material transfer and tribochemical effects depending on mechanical and thermal conditions generated on the wear zones. Transfer layer formation with different morphologies was distinguished to occur at the rake-chip interface.

X 2 CrNi 18 9 austenitic stainless steel material with web and flange thickness of 6 mm was welded by conventional GMAW and double channel shielding gas method (DMAG) to form double fillet T-joints. The differences between these two methods were characterized by measurements of mean welding parameters, thermal camera temperature measurements, Vickers hardness profiles and bead geometries of the joints. Results show higher mean current but lower mean voltage using double channel shielding gas method. Vickers hardness differences between the two methods were insignificant. Moreover, molten mean filler metal area was larger with double channel shielding gas method, which depicted that welding speed for the same filler metal deposition could be increased and this could yield increased productivity.

This work is concentrates on the experimental and analytical study of 7075-T6 aluminum alloys in turning operations. The results are analyzed in terms of surface roughness of the workpiece machined using carbide inserts. Taguchi's experimental design method and analysis of variance (ANOVA) are employed to analyze the effect of cutting parameters on surface finish values. It is demonstrated by the experiments that feed rate affects the surface quality more than the depth of cut and cutting speed. The correlations between the factors and surface roughness are determined by multivariable regression analysis which was developed to predict the surface roughness using the test data. Multivariable regression and prediction used with Taguchi results are compared using statistical methods. Taguchi method gives an approximation with 1.15 % error and produces the better results compared to multivariable regression. Experimental study shows that an increase in feed rate causes adhesion of the aluminum on the tool insert. The amount of stuck aluminum adversely affects the quality of the surface.

The failure testing and repair of composite pipes using different fracture models and different orientation angles under internal pressure was experimentally investigated. Patches with different dimensions were made from composite material for repair. Fracture models on composite pipes were created for three different angles. These are horizontal crack, vertical crack and inclined crack. Adhesive layers created by using DP 410 for repair and failure testing of the composite pipes with different fractures were carried out. Failure loads were obtained from experimental tests. The shear extension coupling of composite pipe and patch was considered because the lay-up angles with + θ and – θ layers were in different radii. Effects of orientation angles and types of fracture models were investigated regarding interaction between the pipe, the adhesive and the patch. The most effective patch width and orientation angles were determined.

The study examines the changes of the microstructural, mechanical and conductivity characteristics of the titanium alloy Ti6Al4 V as a result of heat treatment using wire electrical discharge machining, and their effect on machinability. By means of optical microscopy and scanning electron microscopy (SEM), analyses have been performed to determine various characteristics and additionally, microhardness and conductivity measurements have been conducted. Material removal rate (MRR) and wire wear ratio (WWR) values have been determined by using L 18 Taguchi test design. The microstructures of the samples have been changed by thermal procedures. Results have been obtained by using the Grey relational analysis (GRA) optimization technique to solve the maximum MRR and minimum WWR values. The best (highest) MRR value is obtained from sample E which was water quenched in dual phase processing. The microstructure of this sample is composed of primary α and α’ phases. The best (lowest) WWR value is obtained from sample A.