Volume 64, Issue 12

Morphological evolution of gamma prime precipitates was governed by an elemental partitioning ratio between the gamma and gamma prime phases. In the present study, Ni-based MGA 1400 alloy was modified by adding 4 wt% of Re and 6.4 wt% of Co by vacuum arc melting. The effects of Re and Co additions on lattice parameters of gamma and gamma prime phases were studied by TEM and XRD techniques. Calculated lattice misfit values obtained from XRD and TEM techniques were used to identify the shape and morphology of gamma prime precipitated particles after long-term exposure at 1173 K for 1800 ks? After long-term exposure, gamma prime particles became much coarser. The addition of Re retarded the coarsening rate of the gamma prime precipitates, resulting in smaller gamma prime particles at the same annealing times. Even though, both Re and Co atoms are strongly partitioned in the gamma matrix, the effect of Re and Co additions on lattice misfits was contradictory. The addition of Re produced rounded corner cuboidal morphology of gamma prime precipitates due to higher magnitude with negative lattice misfit (−0.3857%), while Co addition provided a more rounded shape of gamma prime particles due to the lattice misfit value approach to zero (+0.0936%).

The present research work studied and evaluated conditions of pre-weld and post-weld heat treatments for the laser welding process, aiming to avoid weld cracking, which usually occurs after tungsten inert gas and/or laser welding processes in cast nickel-based superalloys with high aluminum and titanium contents. The pre-weld heat treatment conditions used in the experiments were (1) 1473 K for 7.2 ks, (2) 1433 K for 7.2 ks + 1298 K for 56.7 ks, (3) 1413 K for 7.2 ks + 1298 K for 56.7 ks, (4) 1393 K for 7.2 ks + 1298 K for 56.7 ks. A laser welding process on cast nickel-based superalloys, grade GTD-111, with metal filler of Inconel 718, a nickel-iron based alloy was conducted. From all obtained results, it was found that the pre-weld heat treatment conditions significantly influence microstructures before laser welding. After laser welding and post-weld heat treatment at a temperature of 1473 K for 7.2 ks followed by precipitation aging at a temperature of 1118 K for 86.4 ks (standard heat treatment), all welded specimens exhibited similar microstructures and hardness values. Furthermore, no weld cracking was observed in all welded specimens.

In this study, titanium–niobium (Ti-Nb) alloy samples containing β , α ′′, ω and α ′ were used to investigate the effect of each phase on the mechanical properties. The results show that the content of each phase affects the shape of the tensile curve. When the fraction of ω  phase is relatively large, the tensile curve exhibits obvious upper yield point and lower yield point. However, the fraction of α ′′ phase is relatively large; the tensile curve has a single peak yield stage. A small amount of α ′ phase can significantly improve the yield strength, however, the elongation decreased significantly. In addition, some ω phase surrounded in α ′′ matrix was also observed, and it can be inferred that the micro-crack may first appear at the incoherent ω / α ′′ interface under the application of external stress.

In this study, the effect of pure Ni and Ni–SiO 2 nanocomposites coatings on corrosion, wear resistance and thermal conductivity of 316 stainless steel substrates was investigated with the purpose of extending the service life of 316 stainless steel plate heat exchangers. The nanocomposite coatings were developed by electroplating process in a Watts bath in different concentration values of SiO 2 nanoparticles (10, 20 and 30 g l −1 ). Electrochemical corrosion was run to examine the corrosive performance of the coatings. The results showed that the Ni–SiO 2 nanocomposite with concentration of 30 g l −1  had a higher corrosion resistance. A pin on disk wear test demonstrated that, in comparison to 316 stainless steel, the wear resistance of the Ni–SiO 2 nanocomposite (30 g l −1 ) was up to 25% lower while its friction coefficient was almost the same. In addition, as measured via the laser flash method and differential scanning calorimetry, the thermal diffusivity and specific heat capacity of the sample respectively were found to be 32 and 43% lower in comparison to 316 stainless steel. Microhardness measurement via a Vickers microindenter showed that the microhardness of the Ni–SiO 2 nanocomposite coating was more than three times higher than that of 316 stainless steel for all the reinforcement concentrations.

Organic coatings are used as one of the key surface protection methods to protect cast iron pipelines against corrosion due to their cost efficiency and a variety of applications. In most metallic systems that are protected by organic coatings, the performance depends on the response of the coating to corrosion stresses to which they are exposed during operation. One of the most dangerous factors causing chemical damage to coatings are the acidic and chloride aggressive media. Such damage reduces the protection effectiveness thus leading to blistering, cracking, increase in pore volume and number, as well as loss of adhesion. Moreover, the influence of aggressive media impairs also aesthetic characteristics. In the experimental part of the paper, analyses of the physical and chemical properties of epoxy coatings applied on the metal substrate in phosphoric acid, acetic acid and 3.5 wt% NaCl solutions were carried out. The test results showed that the physical properties of epoxy coatings were satisfactory in the acidic medium, but electrochemical tests in 3.5 wt% NaCl solution showed reduced corrosion protection.

Electron beam welding of TC4 titanium alloy and 4J29 Kovar alloy was performed by using different thicknesses of silver interlayers. The microstructure and the composition of welded joints were characterized by scanning electron microscopy, X-ray diffraction, and energy-dipersive spectrometry. The mechanical properties of welded joints were evaluated by tensile strength tests. The results indicated that Ag thickness has great effects on the weld appearance, microstructure, and mechanical properties of electron beam-welded joints. In case of 0.3 and 0.4 mm thickness of Ag interlayers, a considerable part of 4J29 and TC4 melts and a large amount of Fe, Ti, and Ni elements diffuse into the molten pool forming intermetallic compounds (IMCs) such as TiFe 2 , NiTi, and FeTi. In case of 0.6 mm thickness of Ag interlayer, the welded joint exhibits brazing characteristics with little IMCs near the fusion line of 4J29 Kovar alloy side. When the thickness of the Ag interlayer increases to 0.8 mm, the diffusion of Ti and Fe elements is completely inhibited by Ag. As the thickness of the Ag interlayer increases from 0.3 to 0.8 mm, the tensile strength of the welded sample shows a phenomenon that first rises and then falls, and the largest tensile strength is 243 MPa.

Protecting metal surfaces with organic coatings is one of the most common ways of corrosion protection. The main goal of coating is to insulate the base of the material from the corrosive environment in order to provide long lasting protection. The aim of this research is to show how different coating applications in combination with different drying methods affect the coating surface topography. Two different two-component primers were also observed, one containing zinc in its chemical composition and the other one not, to see if zinc had any effect on the surface topography. The surface topography of coatings is examined by the atomic force microscope. At the nano level, the surface condition is quantitatively described by areal topography parameters, also known as 3D roughness parameters. An accelerated laboratory test in the salt spray chamber was performed to compare topography parameters and evaluate which coating system had the slightest differences in observed parameters before and after exposure to a corrosive environment. All the results were statistically processed and presented.

This paper aims to validate the viability of friction stir welding process (FSW) to join high strength aerospace grade AA2014-T6 aluminium alloy for manufacturing light-weight combat aircraft (LCA) structure as a replacement to riveting process. FSW is used to overcome the heat input-related problems in fusion welding of AA2014-T6 aluminium alloy such as coarse grain fusion zone microstructure, softening in HAZ and lower joint efficiency. The 2 mm thick AA2014-T6 aluminium alloy sheets were used as the base material (BM). Friction stir butt (FBW) and friction stir lap (FLP) joints were developed, and its performance was compared with double cover riveted butt (DRB) joint in butt (RBJ) and lap (RLJ) joint configuration. Results showed that the load-carrying capability of FSW joints is greater than the riveted joints. The superior load-carrying capacities of FBW and FLW joints refers to evolution of refined grains and strengthening precipitates in stirred zone (SZ), which ensures superior metallurgical bonding between the joining surfaces. The riveted joints disclosed inferior load-carrying capacities due to the lack of metallurgical connection between the joining surfaces.

This study focuses on the manufacturing of hybrid functionally graded metal matrix composite (HFGMMC) using Al7039 alloy matrix phase which is used as armor material in today’s world. In this context, manufacturing stages of matrix material were analyzed, and necessary parameters were determined for remanufacturing using casting method. With the determined parameters, the matrix material was reinforced by SiC, Al 2 O 3, and B 4 C particles in different volume rates at an average size of 3–10 µm using stir casting method. Three metal matrix composite (MMC) plates which were manufactured using different reinforcement particles in different volume rates were joined as semi-solid with the effect of temperature and pressure in a specially designed mold. In order to complete the manufacturing process, hot forging, and heat treatment were applied to the manufactured composite plate in accordance with the parameters determined in the manufacturing of the matrix. The manufactured MMC and HFGMMC plates were compared in terms of their micro structure, micro hardness, tensile strength, and wear behavior. Finally, HFGMMC plates were joined together by friction stir welding (FSW) in order to analyze their micro structures and mechanical properties after welding.

This study investigated the effects of shallow and deep cryogenic treatment on the microstructural and mechanical properties of Sverker 21 tool steel. After conventional heat treatment, shallow cryogenic treatment at −80 °C for 2, 12, and 24 h and deep cryogenic treatment at −180 °C for 2, 18, and 36 h were applied on the steel samples. After that, the samples were tempered at 200 °C for 2 h. As a result of these treatments, the steel samples’ hardness, toughness, and wear rate changes were determined, and their microstructural properties were investigated. As a result of the study, it was observed that the cryogenic treatment had positive effects on the mechanical and microstructural properties of Sverker 21 steel. Mechanical properties also improved with increasing holding time for both cryogenic treatment types. It has been found that the deep cryogenic treatment provides better mechanical properties compared to the shallow cryogenic treatment. The maximum hardness and wear resistance were obtained in the deep cryogenically treated sample for 36 h. Compared to the CHT sample, the hardness and impact energy of the DCT(36) sample increased by approximately 11.75% and 17.36%. An improvement of approximately 64% was observed in the wear rate.

A self-designed Ti–Zr–Cu composite foil was used as an interlayer and vacuum brazed to achieve a heterogeneous joint between the Cf/SiC composite and Nb, resulting in a well-bonded, defect-free joint with a typical interfacial microstructure of Cf/SiC/(Ti, Zr)C/(Ti, Zr)2Cu + Zr2Cu/Ti2Cu + (Ti, Nb)ss/Nb. The effects of different experimental temperatures on the microstructural evolution of the joints and the mechanical properties of the joints were investigated, and the formation mechanism of the joint interface was analyzed. The results show that the microscopic morphology and mechanical properties of the joint interface change significantly with increasing experimental temperature. As the temperature increased to 1080 °C, the shear strength increased by 150.6% compared to 1060 °C (78.09 MPa) and reached a maximum value of 195.72 MPa, but further warming to 1100 °C (144.25 MPa) resulted in a 26.3% decrease in shear strength, with the best joint achieved at 1080 °C.

In this study, the wear behaviour of the composite material obtained as a result of the coating process by adding nano-size powder to the consumable rod with the friction surfacing method was investigated. An amount of 3–5 wt% nano graphene and carbon nano tube (CNT) were added into the hole drilled at a certain depth in the center of the consumable rod, and then the rod was subjected to sintering process. The obtained consumable rod was deposited on the substrate material at a certain rotational speed, horizontal and vertical progression speeds by friction surfacing method. Wear tests were carried out by subjecting the deposited surface samples to the pin-on-disc wear test. According to the results obtained, the increase in the additive ratio decreased the wear rate by approximately 30% in the 3 wt% graphene additive sample and 75% in the 5 wt% additive sample for 900 m wear distance. The same CNT additive ratios decreased the wear rate in the sample by 41% and 58%, respectively.

In this work, the change on the microstructure and mechanical properties of high chromium steel investigated by adding ultra-high boron contents. Specimens produced by casting method. A total of 430 type martensitic stainless steel scraps melted in an induction furnace where the chemical composition of melt controlled (by adding ferro alloys, de-oxidation, removing nitrogen, etc.). At 1550 °C, melt was poured into sand molds with the shape of Y blocks. Wet chemical analysis was used for boron analysis. The change on the microstructure and mechanical properties (hardness test, Charpy impact test and pin on disc abrasive wear test) determined. Experimental results revealed that, martensitic matrix obtained in both boron free steel and ultra-high boron steels. Chromium carbides and borides were embedded each other (M 2 B and M 7 (C, B) 5 type of carbide/borides) according to X-ray diffraction results. With the change of boron content, carbide/boride volume fraction, distribution and shapes were changed as well. Hardness and abrasion resistance improved for the steels having higher boron contents however impact toughness deteriorated significantly.

The main objective of this investigation is to study the microstructure, tensile properties and fracture toughness of friction stir welded (FSW) butt joints of 10 mm thick AA7075-T651 plates. The microstructural features of stir zone (SZ), thermos-mechanically affected zone (TMAZ), heat affected zone (HAZ) were analyzed using optical microscopy technique. The tensile properties were evaluated using smooth and notch tensile specimens and compared to base metal properties. The microhardness survey was done across the weld cross section and correlated to the failure of tensile specimens. Compact tension (CT) specimens were used to evaluate the fracture toughness of welded joints. The fractured tensile and CT specimens were analyzed using scanning electron microscopy (SEM). Results showed that the FSW AA7075-T651 specimens welded using axial load of 12 kN, tool rotation speed of 750 rpm and welding speed of 30 mm/min exhibited 412 MPa tensile strength and 9% elongation. It showed 88 and 89% of base metal strength elongation. The joints showed fracture toughness of 23 MPa m 1/2 which is 80% of base metal fracture toughness. The superior tensile and fracture toughness properties of joints are mainly attributed to the evolution of finer grains in SZ due to the stirring action of FSW tool.

In this study, NiTi and NiTi-XSiC (1 wt%, 2 wt%, and 4 wt%) powders were coated on the Ti6Al4V surface by the self-propagating high -temperature synthesis (SHS) method using induction heating. Optic microscope and a scanning electron microscope (SEM) for the microstructural properties of coatings, energy dispersive spectrometry (EDS) for element distribution analysis, and X-ray diffractogram (XRD) for phase component analysis were carried out. The microhardness difference between the coating and the substrate was assessed by using the Vickers hardness scale. The microhardness increased with the addition of SiC, and the highest hardness value was 1416 Hv and detected in the sample NiTi–SiC 4 wt%. Phases formed by diffusion during solidification in the compounds Ti, Al, NiTi, NiTi2, NiAl, Ni3Al, Al3Ti, and TiO2, respectively.

The main aim of this article was to develop new glaze receipts (NGRs) to build up the acid resistance (AR) of commercial glazes (CGs) used in floor tile production. The glaze is a vitrified material that melts the surface of the ceramic material. Improvements were made during and after the manufacture, based on the glaze samples of the CGs. NGRs were synthesized using different mineral compositions. AR, density, chemical, and physical properties of commercial and new synthesized glazes were determined using X-ray diffraction, scanning electron microscopy/energy-dispersive X-ray spectroscopy, Fourier transform infrared spectrometry, and water contact angle analysis methods. The AR of the obtained samples (standard and developed floor tiles) was examined by treating them with 3% HCl for 3 days. Results showed that synthesized glazes had higher AR than standard glazes (CGs). The NGRs also significantly improved the ceramic surface coating features of the new glazes.