Volume 62, Issue 12

In this contribution, particle sizes of TiC (13 and 93 μm) and volume fractions of ZrC (5 and 10 vol.-%) with respect to reinforcement particles were varied to investigate the effects on the microstructure, hardness, density, wear and corrosion properties of AZ91 Mg matrix alloy. Experimental results revealed that the hardness, density and sliding wear performance of AZ91 alloy were markedly improved by the addition of carbide particles. Predominant wear and corrosion mechanisms were identified considering the size and volume fraction of the carbides. The composite sample comprising fine TiC particles (13 μm) exhibited the highest wear resistance at the same volume fraction as the coarse particles. Moreover, coarse ZrC particles with a low volume fraction (5 vol.-%) provided an enhanced wear resistance beyond that of the 10 vol.-% ZrC particles. Considering all the investigated composites, the corrosion resistance of the composites deteriorated with the increasing volume fraction and size of the carbide particles. Electrochemical measurements of the 0,5M NaCl solution revealed that increasing carbide particle size and volume fraction leads to lower corrosion resistance due to the formation of more cathodic areas which are preferred sites for the initiation of pitting corrosion.

In this study, the goal is to determine the types of steel rope best used in environments such as harbors and on ships, by examining the behavior of different types of steel wire hoisting ropes used in cranes with respect to corrosion. Initially, hemp and steel wire core ropes were taken from 6 × 19 Standard, 8 × 19 Seale and 6 × 36 Warrington Seale rope groups that have the same diameter. Corrosion resistance was compared in these ropes through the application of three methods. According to the first method, corrosion resistance was examined via change in material mass. For this purpose, ropes were subjected to an accelerated aging test in an aging test cabin in accordance with ASTM B117 standard for one month for each aging process. 3 different 30-day processes were followed with 24-hour cycles. Corrosion exposure rates differed for each process. After going through the aging process, the damage suffered by the ropes was determined via visual inspection and the impact left by corrosion was evaluated by examining the mass changes seen in the ropes before and after aging for each process. The Tafel extrapolation, which is an electrochemical test, was applied in the second method. E corr and I corr values of the ropes as well as their corrosion rates were determined and compared. Corrosion behavior was investigated in the third method through the application of mechanical experiments on aged steel ropes. In conclusion, corrosion resistant hoisting ropes were identified by comparing the results attained from the three methods.

A milling induced deformation layer of Z3CN20.09M, 304L and 316L austenite stainless steel (SS) was investigated by electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and a nanoindenter. The results indicated that the deformation layer was formed with a depth of about 200 μm, including a nanocrystalline layer within the range of 3 μm at the subsurface and followed by a large amount of persistent slip bands (PSBs). The significant plastic deformation was observed on the cross section of deformation layer with a range of about 80 μm for Z3CN20.09M and 304L SS, while being only about 30 μm for 316L SS. The highest residual stress tested on the milled surface reached about 1000 MPa, which can be attributed to the fact that a deformed martensite phase was formed at the surface during the milling operation. The nanohardness increased by 20-60 % on the cross section of the deformation layer as compared to the matrix.

Traffic accidents are increasing as a result of an increasing number of vehicles and population growth in recent years. Active and passive safety systems are used in the vehicles we use today to reduce traffic accidents and prevent casualties. One of the passive security systems is the crush box (crashworthiness). It absorbs the energy generated during a crash by plastic deformation. In this study, tube height, diameter and thickness parameters were kept constant and degrees of conicity were varied 0°(flat tube),3°,7°,10°,12° and 15° The effects of conical crush boxes on axial crush behavior and their energy absorption ability, were investigated by Ls-Dyna explicit dynamic software.

Ramor 500 steel plates are used as a ballistic material due to their greater hardness and strength properties. This steel can be produced with a 2-30 mm thickness sheet which may attain 505-590 HV hardness. In the present work, Ramor 500 steel pairs are joined using a submerged arc welding (SAW) process and taking various parameters into consideration. An austenitic additional wire is used for the welding process which contains Cr, Ni, and Mn. The source model prototype was developed using ANSYS software and considering a time-dependent three dimensional thermal model with source cooling. The highest tensile stress voltage value was determined in the sample applying a constant current of 250 A, 25 V and 30 cm × min -1 welding speed. It was observed that the welding seam width increases as welding tension grows and that welding height and depth increase and decrease more or less in tandem. A ANSYS thermal cooling analysis revealed that welding tension grows with heat transfer which increases 15 mm from the main center of the welding area.

MoNiAl-WC reinforced Fe matrix composites were obtained by mechanical alloying. The effect of various reinforcement ratios on microstructure change, elemental characterization and phase transformation were examined by using optical microscopy, scanning electron microscopy, energy dispersion spectroscopy, X-ray diffraction, elemental surface mapping and a microhardness test. Fe and MoNiAl-WC compound and powder mixtures were synthesized by MA and nanocrystalline solid solution was obtained. The increase in the reinforcement ratio reduced grain size in the structure and increased the carbide ratio. The composite demonstrated excellent metallurgical qualities and interface bonding. Moreover, it was found that the amount of porosities increased with increasing reinforcement. X-Ray analysis showed the formation of NiAl, Al 3 Ni and WC phases.

In this paper, a copper-based bond emery wheel was prepared by vacuum hot pressing sintering through powder metallurgy. The effects of various bond contents on the grinding performance of the copperbased bond grinding wheel were studied using a self-made experimental device; the friction coefficients between the friction pairs and roughness of the grinded rail surface were also obtained. The results show that the grinding wheel had the best grinding performance when the content of the copper-based bond was at 35 wt.-%, the friction coefficient 0.29, the grinding ratio 81.34, and the surface roughness 7.191 μm, which meet the roughness requirements of rail grinding. The microstructure of the rail surface and debris after grinding were studied by scanning electron microscope and energy spectrum analysis. Adhesive wear, abrasive wear, oxidation wear and delamination wear occurred during the friction and wear process. The grinding behavior of grinding wheels was analyzed in accordance with the experimental results.

To reduce the fuel consumption and enhance the flight performance of satellites, it is desirable to employ structural components of low weight, high strength, and high stiffness. Therefore, most primary and secondary structures of satellites are built using sandwich panels. Fasteners, which constitute secondary structures, are normally used as joining parts in different types of inserts such as partially potted, fully potted, and through-thickness inserts. Finite element analysis (FEA) is valuable for predicting the behavior of such primary and secondary structures. However, to obtain more realistic results from such analysis, it is necessary to define suitable fastener stiffness values. To this end, in this study, a method for calculating the fastener stiffness of a fully potted insert for sandwich panels using a finite element model is exemplarily developed and experimentally validated. In addition, a shell modeling is established for various connection types to further save time and reduce the computational cost of the finite element model. Finally, the effects of the fastener stiffness on the numerical analysis results for satellite structural system are evaluated. The two-dimensional (2D) structure modeling method used in this study was found to be as fully sufficient as three-dimensional modeling. In addition to saving time and cost, 2D FEA numerical modeling and prediction could reduce elaborate test costs.

Ni-based superalloys are well established in various industrial applications, because of their excellent mechanical properties and corrosion resistance at high temperatures. Despite the high development stage and a common industrial use of these alloys, hot cracking remains a major challenge limiting the weldability of the materials. As commonly known, the hot cracking susceptibility during welding increases with the amount of precipitation phases. Hence, a large amount of highstrength Ni-Alloys is rated as non-weldable. A new approach based on electron beam welding at low feed rates shows great potential for reducing the hot cracking tendency of precipitation-hardened alloys. However, geometry and properties of the weld seam differ significantly in comparison to the common process range for practical uses. The aim of this study is to investigate the influence of welding parameters on the seam geometry at low feed rates between 1 mm/s and 10 mm/s. For this purpose, 25 bead on plate welds on a 12 mm thick sheet made of Inconel 718 are carried out. First, the relevant parameters are identified by performing a screening. Then the effects discovered are further studied by using a central composite design. The results show a significant difference between the analyzed weld seam geometry in comparison to the well-known appearance of electron beam welded seams.

In this study, the mechanical behavior of composite pipes joined with embedded and non-embedded adhesive layers is investigated. Due to their high resistance, corrosion resistance, repair and lightness, composite materials have been used in industry increasingly. In general, composite pipes are used for the transport of pressurized liquids and gases. Joining processes are performed using many different methods. This study is intended to facilitate the joining process of composite pipes and to increase their applicability. In this study, the development of various bonding methods were investigated using composite pipes and double reinforced structural adhesives. Likewise stress behavior was analyzed. Generally, models with patch and patch quality are found in the literature.In this study by contrast, joining operations will be made easier by means of composite pipe joining models designed using glue without a patch. As a result, time and extra cost savings can be achieved.

Low alloy and stainless steel are the most used types of iron-based materials world wide. Their use against in machine element work, reclamation, corrosion and wear resistance are still challenging. To overcome this problem, many steel alloys are coated with cermet coatings to protect the parts from wear and corrosion. In the present study, WC-Co and WC-CoCr coatings were applied by means of a high velocity oxy-fuel (HVOF) technique on AISI 304, AISI 1040, and AISI 4340 steel alloys used as substrates. The aim was to investigate surface properties and wear resistance of the coatings and to determine their relationship with the type of coating and substrate. In accordance with this purpose, hardness and thickness of the coatings were measured, sliding wear tests were performed, scanning electron microscope (SEM) images and X-ray diffractions (XRD) were taken, surface roughness and friction coefficients were determined. The results showed that the WC-CoCr coatings had higher hardness and lower thickness than the WC-Co coatings. Maximum hardness was obtained in the WC-CoCr coating applied to AISI 4340 steel, which was also the hardest alloy among those studied. After wear resistance tests, it was revealed that the wear resistance of the WC-CoCr coatings was better than that of the WC-Co coatings for each steel substrate. During the coating, the new phases resulting from the decomposition of the WC phase in the WC-CoCr coatings contributed more to wear resistance than those of the WC-Co coatings. A lower friction coefficient and lower surface roughness of the WC-CoCr coatings during wear were obtained, resulting in higher wear resistance. A WC-CoCr coating on AISI 4340 alloy which has the highest hardness, lowest surface roughness and lowest friction coefficient resulted in the highest wear resistance among all types studied.

In this study, the tribological properties of 7075 aluminum alloy produced by ultrasonic melt treatment (UST) are investigated. Tribological properties of untreated and ultrasonically treated samples under dry and lubricated sliding conditions were analyzed experimentally by the block on ring test method. Worn surfaces of untreated and ultrasonically treated samples were scanned by 3D optical profilometer and analyzed to search out wear characteristics in the material. Furthermore, microstructural examinations were conducted to investigate the beneficial effects of UST on the microstructural properties of the alloy using optical and scanning electron microscopy. According to the results obtained, UST refines the α-Al phase of the alloy and disperses precipitates to grain boundaries more uniformly. Also, hardness and density of the alloy increased through the effect of UST. Due to these favorable effects, the wear resistance of the alloy increased and the worn surfaces of the ultrasonically treated samples exhibited lower surface roughness according to 3D surface roughness measurements.

SiAlON ceramics and their derivatives are potential materials for tribological applications where wear and friction are very crucial. TiN is a reinforcement phase and solid lubricant for SiAlON used to improve mechanical and tribological properties. In this study, α ı :β ı -SiAlON composites incorporating nano- and micron-size TiN particles were produced by a gas pressure sintering method. Tribological behavior of the composites was investigated based on reinforcement particle size and physico-mechanical properties. Tribology tests were performed with a computer-controlled tribometer under dry unlubricated conditions with ball-on-disk configuration. It was found that the TiN particle size has an effect on surface roughness and hence the coefficient of friction. When the TiN particle size decreased to nano size, the wear mechanism was tribochemical, whereas, when the particle size increased to micron size, severe mechanical wear was observed besides tribochemical wear.

Recently, many applications have used austempered ductile iron due to its high hardness, strength, toughness, and wear resistance. These superior properties make austempered ductile iron an alternative material to forged steels. However, machining of austempered ductile iron is challenging because of its high hardness and strength. In this study, machining operations were performed on the alloyed ductile iron workpiece to investigate the machinability of the material prior to the austempering process. This experimental study was carried out on EN 1.7131 alloy steel and alloyed ductile iron using single point carbide inserts under dry cutting conditions. A constant feed of 0.1 mm × rev-1, constant depth of cut of 1 mm, and variable cutting speeds were selected as input parameters, whereas tool life is considered as a response parameter. The tool life tests were accomplished considering flank wear as tool life criterion according to ISO 3685. The results of this study indicated that although the machinability of ductile iron is 88 % of the normalized forged EN 1.7131 steel for a 60 minutes’ tool life, identical tool life was observed for both materials at 96 m × min -1 cutting speeds.

In the study conducted for this contribution, sheet material 4 mm thick, non-heat treated (II), normalized (NH) and tempering heat treatment implemented (TH), were formed at a bending angle of 90°. As a result of the forming process, the effects of the R2, R3, R4, R5, and R6 mm punch tip radii on spring back and spring go values were investigated. The bending operations were carried out by waiting for the punch in the material bending zone for 30 sec and then lifting. The samples were extracted from the middle deformation zone of the II, NH and TH applied sheet material, to which the bending process was applied, following which their ferrite phase, pearlite and martensite structures were microstructurally analyzed. A Minitab analysis program was used to investigate the effect of the bending parameters on the sheet material’s spring-back and spring-go behavior. Moreover, the effects of bending parameters were investigated by creating numerical and mathematical models. Thus, it was determined that spring-go behavior occurred on the II and NH applied sheet material, while spring-back behavior occurred on the TH applied material.