Volume 62, Issue 11

Laser cladding Ni-based WC reinforced composite coating was fabricated on the surface of Q235 steel using 6 KW fiber laser. The morphology, composition, microhardness and wear resistance of the composite coating at varied contents of WC particles were studied using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), microhardness tester and a wear tester. The results show that the dilution rate of the cladding layer decreases first and then increases with an increase of WC content. When the WC content is 20 wt.-%, the dilution rate is the smallest. In the process of fiber laser cladding Ni-based WC reinforced composite coating, WC particles partially dissolve and interact with other elements to form eutectics, which exist as lumpy shapes, strips and as spherical shapes. By increasing the WC content, the structure of the cladding layer appears to be refined. The main phases of the laser cladding layer are γ-Ni, M 7 C 3 , M 23 C 6 , CrB, WC and W 2 C. As the WC content increases, the hardness of the cladding layer increases. When the WC mass fraction reaches 40 wt.-%, the average hardness of the composite coating can be more than five times the substrate. When the mass fraction of WC is 20 wt.-%, the wear resistance of the cladding layer is best, which is more than three times that of Ni60A coating.

A gas cylinder, containing carbon dioxide (CO 2 ) in a manifold of sixteen cylinders, exploded in an outdoor building construction site at midday within two hours of its arrival from a filling station. It was to be used for construction welding. The seamless gas cylinder that exploded was made of low alloy steel with a tempered martensitic microstructure. Observation revealed the presence of discreet localized external corrosion which weakened the gas cylinder extremely. A study concluded that the midday outdoor heat had apparently increased the pressure of the carbon dioxide gas within which in turn led to the sudden catastrophic explosion of the weakened corroded gas cylinder.

The aim of this study was to coat different types of Stellite (1, 6 and 12) whose carbon rates vary on Hardox 450 and St 52 steel by means of tungsten inert gas (TIG) welding. For the purpose of microstructure investigations after welding, SEM, EDX, X-Ray and microhardness tests were carried out. It was observed that different types of Stellite coating with different features have an effective influence on microstructure and in the presence of dendritic nets between the grains decreased when the carbon content in Stellite coating decreased and when the substrates varied. In addition, it was determined in microhardness examinations that hardness increased with increasing carbon content and that the highest hardness value of 762 HV in sample S1 was attained. Consequently, positive results have been given for coating Hardox 450 steel and St 52 steel with Stellite via the TIG method.

Iron based composite materials reinforced with various ceramic particles are used in operating conditions requiring features such as high hardness, strength and wear resistance. The composite materials may be subject to corrosion depending on the working environment. In this study, the corrosion properties of iron based composite materials produced by powder metallurgy, containing carbon and different amounts of alumina reinforcement were investigated. In the materials production, 0.5 wt.-% carbon and 1, 3 and 5 wt.-% alumina powders were added to the iron powders as reinforcement. Followed by mixing, one-way cold pressing and sintering, respectively, both iron based carbon and alumina reinforced composite samples were obtained. The electrochemical corrosion properties of iron based composite materials containing various amounts of alumina reinforcement were investigated in a 3.5 wt.-% NaCl environment and the effects of the reinforcing material ratio on the corrosion behavior of the composite material were determined. It was determined that with an increase in the alumina reinforcement ratio, the corrosion rate of the material increases and the corrosion resistance decreases.

Inconel 718 is a nickel-based superalloy, typically used in high temperature aerospace applications due to its exceptional mechanical properties and weldability. However, it is susceptible to solute segregation and coarser interconnected laves phase evolution in weld metal due to the high heat input in the gas tungsten arc welding (GTAW) process which drastically reduces the tensile properties of welded joints. It is also susceptible to HAZ microfissuring and liquation cracking issues owing to the evolution of low melting temperature eutectic film at the grain boundaries. To overcome this problem, a newly emerged novel gas tungsten constricted arc welding (GTCAW) process, principally differentiated by magnetic arc constriction and high frequency accentuation of the arc, is used to join Inconel 718 superalloy. The primary objective of this investigation is to evaluate the microstructural characteristics and tensile properties of GTCA welded Inconel 718 superalloy sheets (2 mm thick), fabricated using optimized process parameters, and compare its performance with the base metal. Results showed that GTCA welded joints exhibited 99.20 % and 73.5 % of base metal strength and ductility claiming significant advantages over the GTAW process. It is correlated to the grain refinement in the fusion zone and the evolution of finer discrete laves phase in interdendritic areas of the weld. The basic mechanism responsible for fusion zone grain refinement and corresponding influence on tensile properties of joints is also discussed in brief with regard to the mechanics of arc constriction and pulsing.

The present study aims to investigate the feasibility of friction stir spot welding two dissimilar polymers, acrylonitrile butadiene styrene and polycarbonate. Welding parameters are effective on lap joint shear load. This study also investigated the influences of welding parameters such as rotational speed, plunge depth, and dwell time on the joint morphology and mechanical characterization. In addition, a common problem in friction stir spot welding is the forming of characteristic keyholes in the joint,s a problem that has an important effect on mechanical test results. For this reason, a polycarbonate filler sheet was used to improve the lap joint shear load by reducing the size of the keyhole in this study. The quality of the welded specimens was examined after lap joint shear tests. Experiments were carried out according to Taguchi L 9 orthogonal array using a randomized approach for arranging optimum welding parameters. Signal-to-noise ratio and the analysis of variance were used to determine the influences of each process parameter on the lap joint shear load. Results indicated that the friction stir spot welding of acrylonitrile butadiene styrene with polycarbonate is feasible and welding parameters significantly affected joint quality. From the experiments, a 57 % improvement was achieved in the lap joint shear load from the initial welding parameters to the optimal welding parameters. Furthermore, weld morphology was investigated by morphological analysis and visual comparisons. Finally, the failure modes of the fractured samples were observed and classified for highest, moderate, and lowest lap joint shear loads.

In this paper, the dielectric properties of a series of glyceryl monoolein/ water liquid crystal systems containing 15, 20, 25, 30, 35, 40, 45, and 50 wt.-% water are measured between 90 and 140 GHz. An IEEE standard WR-08 waveguide shim is used as a sample holder. The holder is filled with the monoolein/water liquid crystal system during measurement. The S-parameters of the sample holder filled with the liquid crystal systems are measured using 90-140 GHz millimeter-wave test equipment. The dielectric properties of the crystal systems are extracted from the measured transmission parameters (S 21 ) using the Newton algorithm. We find that the dielectric properties of these glyceryl monoolein/water liquid crystal systems from 90 GHz to 140 GHz are not sensitive to frequency. That is in contrast to the low-frequency dielectric properties in the literature. We also find that the imaginary component of the dielectric spectroscopy between 90 and 140 GHz can identify the phase of the monoolein/water liquid crystal system. The finds in this paper are important for monoolein study.

The ultimate objective is to evaluate the efficacy of three-dimensional printers (3DP) for manufacturing a rear spoiler for radio-controlled (RC) racing cars. This research work focuses on the development of a multicritaeria decision making (MCDM) model for selecting a 3DP. The selection process includes multiple adverse criteria such as maximum print volume (E1), speed of operation (E2), minimum thickness (E3), extruder capacity (E4), printer cost (E5) and filament material cost (E6). To reduce this adverse nature of the assessment criteria, the preference selection index (PSI) method is anticipated as an MCDM technique for selecting the most suitable 3DP. In this work, ten alternative printers, Lulzbot TAZ 5 (A1), Ultimaker 2 (A2), Zortrax (A3), Wanhao duplicator 4 (A4), Airwolf 3D AW3D HD2X (A5), Flash forge creator X(A6), Makerbot replicator original (A7), Delta non-turbo WASP 2040(A8), Artifex duo 2 (A9), UP plus 2 (A10)are considered for the assessment process. From the suggested PSI models, the Wanhao duplicator 4 (A4) has emerged as a suitable 3DP for RC car application.

The microstructural characteristics of friction welded AISI 316 stainless steel samples in a welding zone and a heat affected zone were investigated. Inhomogeneous plastic deformation occurred due to friction welding. Individual grains in the final microstructure underwent various evolution mechanisms. These were caused by the growth of the initially recrystallized grains or as a result of the dynamic recrystallization of the sub-grains formed. The grains within the welding zone and the heat affected zone exhibited different densities of dislocations and experienced various degrees of recovery. Using reasonable estimates of the strain, strain rate and temperature of the friction welding, the dependence of the dynamic recrystallization grain size was found to have the same dependence on the Zener-Hollomon parameter as material deformed via a conventional hot working process.

In this study, deflection values occurring on the main girder of a portal crane at various payloads were investigated theoretically, numerically and experimentally. The entire portal crane structure was analyzed on via a computer model in order to assess the reliability of the main girder in terms of deflection. Variations in deflection on the main girder were determined in accordance with load lifted and the crane trolley position. In addition, deflection values at critical points on the main girder of the portal crane were measured experimentally. Results indicate that maximum deflection value occurring on the main girder when the crane trolley was located at the middle of main girder were 1.34 times greater than the deflection value when the crane trolley was located at loading position 3.

The present study is devoted to research into the morphology and structural-phase state of an R6M5 high speed steel surface layer after it was affected by a plasma beam. It was discovered, that R6M5 steel is a multi-phase material with an α-phase, γ-phase (retained austenite) and carbide phase just as in the initial state. The main phase component of the R6M5 steel matrix before and after plasma beam processing was an α-phase (γ → α’-martensite): lamellar and lath martensite; but lamellar martensite is dominated by a volume ratio ~90 % gross share α’-martensite. The γ-phase as the second morphological component of the steel matrix (retained austenite) yields within the martensite plates the form of twintype colonies with a volume ratio of ~6 %. It was established that there were М 6 С -type carbide particles of complex composition (Fe,W,Mo) 6 C in the material just as in the initial state. It should be said that in its initial state, the dislocation structure, formed under the effect of the plasma beam, is characterized by fairly high value of excess density of dislocations with an average value of ρ± = 2.0 × 10 10 cm -2 (in the initial state ρ± = 1.7 × 10 10 cm -2 ) along with scalar density. The depth of torsion curve of the face-centered space lattice in the α’-martensite is χ = 500 cm -1 (in the initial state it is equal to χ ~436 cm -1 ), the amplitude of the inner long-distance voltage is σ ∂ = 280 МPа (in the initial state it is equal to σ ∂ = 260 МPа). Thus, the amplitude of shift voltage is equal to σ L = 420 МPа (in the initial state it is σ L = 350 МPа); nevertheless, σ L > σ ∂ remains the mean torsion-curve of the fcs-lattice of α’-martensite maintaining its lamellar nature after the effect of the electron beam much as in the initial state.

Hollow shafts are typically deployed in real world engineering application where strength to density ratio is highly desirable. Introduction of cutouts will also assist in achieving the same, where further material reduction is inevitable. This research work mainly focusses on assessing the impact of introducing cutouts on a hollow shaft system experimentally, followed by numerical validation. In this study the vibrational characteristics of a hollow shaft made up of linear elastic material is compared with a composite one for five different geometric profiles. Obtained results clearly reveal that introduction of cutouts and composite material significantly reduces the natural frequency of the system. Also, the experimental results are well in line with the values derived from the finite element method.

In this study, low superheat casting and cooling slope casting processes were carried out with A356 and A380 aluminum alloys in order to obtain feedstocks with near globular microstructures. Castings were conducted at 20 °C above of the liquidus temperature for both processes and molten alloys were cast through a copper cooling slope with two different lengths (350 mm and 650 mm) and two different tilt angles (30° and 60°). In order to evaluate the significance of boron nitride coating on cooling slope, castings in short slope were carried out under both coated and uncoated conditions. Microstructural examinations and hardness measurements were carried out. According to obtained results, cooling slope casting caused superior microstructural properties as compared to low superheat casting, especially for A356 alloy. 30° tilt angle was found more efficient in order to obtain a more globular microstructure for A356, while, on the other hand, the tilt angle of 60° was detected more favorable in that manner for A380. Obtained grain size measurements were slightly improved with the employment of short slope and coating was found beneficial especially for A356 alloy. The measured hardness values did not display any significant difference in the same alloy type except in the low superheat cast A356 specimen, which was obtained with coarser microstructure.