Effect of Mo addition on microstructure, mechanical and machinability properties of Cr-PM steels

In this work, it was investigated the effect of molybdenum (Mo) addition on machinability, mechanical properties, and microstructure of Cr steels produced by using powder metallurgy method. Tensile and hardness experiments were applied to define the mechanical properties of the produced Cr-PM steels. The machining experiments have been also performed without coolant on a CNC vertical machining center at three different cutting speeds (150, 210, and 270 m/min), two different feed rates (0.4 and 0.8 mm/tooth), and constant depth of cut (0.5 mm). The machinability of the alloys was evaluated in regard to surface roughness (Ra) and tool wear (Vb). The results indicated that that Cr-PM steel with 5% Mo addition by weight had the highest yield, tensile strength, and hardness, and the best surface quality was obtained in this sample in terms of surface roughness. However, according to Vb measurement results, the cutting performance of the cutting inserts wasnegative affected by MoC(N), CrC(N), and MoCrC(N) precipitates formed in the microstructure of PM steel.

Effect of the Laser Surface Treatment on Properties of the Alloy (Ni-Cu-V) Nanoparticles Prepared by Powder Metallurgy Method

In this research, an alloy with a nanostructure was prepared using a metallurgical technique. To prepare an ideal alloy, three nanoscale powders were used (70 percent Ni, 25 percent Cu, and 5 percent V). The dried alloy was stored under 8 Tons of cold pressing at 80°C for 30 minutes. After that, a surface treatment of the prepared alloys with different laser energies (0, 200, 260, 300) mJ was carried out with a pulse time (10 seconds) at a distance of (100 cm). and hardness (Rockwell method) is studied. By immersing samples in a solution (3.5 percent NaCl) for different periods (3, 5, 7, 9, 11) days, the effect of laser surface treatment on the corrosion resistance of the alloy was investigated. Results show that porosity, water absorption ratio decreases after laser surface treatment with rising hardness values. Additionally, the wear resistance decreases as laser energy increases. Atomic force microscope images show that grain sizes increase as laser energy increases, and by increasing the laser energy, the surface of the nanoparticles is more homogeneous. Easy architecture and high nanostructure alloy consistency play a key role in improving the mechanical and physical properties.

Preparation of Sodalite and Faujasite Clay Composite Membranes and Their Utilization in the Decontamination of Dye Effluents

The present work describes the deposition of two zeolite films, sodalite and faujasite, by the hydrothermal method to tune the mesopores of clay support, which are prepared from a widely available clay depot from the central region of Morocco (Midelt). The clay supports were prepared by a powder metallurgy method from different granulometries with activated carbon as a porosity agent, using uniaxial compression followed by a sintering process. The 160 µm ≤ Φ ≤ 250 µm support showed the highest water flux compared to the supports made from smaller granulometries with a minimum water flux of 1405 L.m−2·h−1 after a working time of 2 h and 90 min. This support was chosen for the deposition of sodalite (SOM) and faujasite (FAM) zeolite membranes. The X-ray diffraction of sodalite and faujasite showed that they were well crystallized, and the obtained spectra corresponded well with the sought phases. Such findings were confirmed by the SEM analysis, which showed that SOM was crystalized as fine particles while the FAM micrographs showed the existence of crystals with an average size ranging from 0.53 µm to 1.8 µm with a bipyramidal shape and a square or Cubo octahedral base. Nitrogen adsorption analysis showed that the pore sizes of the supports got narrowed to 2.28 nm after deposition of sodalite and faujasite. The efficiencies of SOM and FAM membranes were evaluated by filtration tests of solutions containing methyl orange (MO) using a flow loop, which were developed for dead-end filtration. The retention of methylene orange (MO) followed the order: SOM > FAM > 160 µm ≤ Φ ≤ 250 µm clay support with 55%, 48% and 35%, respectively. Size exclusion was the predominant mechanism of filtration of MO through SOM, FAM, and the support. However, the charge repulsion between the surface of the membrane and the negatively charged MO have not been ruled out. The point of zero charge (pzc) of the clay support, SOM and FAM membrane were pHpzc = 9.4, pHpzc = 10.6, and pHpzc = 11.4, respectively. Filtrations of MO were carried out between pH = 5.5 and pH = 6.5, which indicated that the surface of the membranes was positively charged while MO was negatively charged. The interaction of MO with the membranes might have happened through its vertical geometry.

Fabrication and Characterization of New Functional Graded Material Based on Ti, Ta, and Zr by Powder Metallurgy Method

In view of the aging population and various diseases worldwide, the demand for implants has been rapidly increasing. Despite the efforts of doctors, engineers, and medical companies, the fabrication of and procedures associated with implants have not yet been perfected. Therefore, a high percentage of premature implantations has been observed. The main problem with metal implants is the mechanical mismatch between human bone and the implant material. Zirconium/titanium-based materials with graded porosity and composition were prepared by powder metallurgy. The whole samples are comprised of three zones, with a radial gradient in the phase composition, microstructure, and pore structure. The samples were prepared by a three-step powder metallurgy method. The microstructure and properties were observed to change gradually with the distance from the center of the sample. The x-ray diffraction analysis and microstructure observation confirmed the formation of diffusive connections between the particular areas. Additionally, the mechanical properties of the obtained materials were checked, with respect to the distance from the center of the sample. An analysis of the corrosion properties of the obtained materials was also carried out.

Sustainable Production of Powder Metallurgy Aluminum Foams Sintered by Concentrated Solar Energy

Porous aluminum foams were successfully fabricated following the space-holder powder metallurgy method with a solar sintering stage. Al foams with porosities of 50, 60, and 70 vol.% were sintered in a low-cost Fresnel lens. Green parts were prepared using aluminum powder as the main metallic material and saccharose as a soluble space-holder. The dissolution stage was designed for each foam and required longer periods of time, between 8 and 32 h, as the design porosity increased. Brown parts were fully sintered by concentrated solar energy at a lower temperature (500 °C) and for shorter times (12–20 min) than those required by conventional sintering techniques (640 °C, ~9 h). The evaluation of density and the characterization of pore size and distribution in the sintered foams was carried out. All obtained foams were stable and presented a homogeneously distributed porosity, very close to the design porosity, with differences lower than 2.1 vol.%, and with approximately half being characterized as open porosity. Moreover, the solar sintered foams presented a high quality, and similar or even greater mechanical properties (such as compressive strength and impact energy absorption) than those achieved by conventional techniques. Foams with 50 vol.% of porosity exhibited the best mechanical behavior, in terms of impact-energy absorption (24.42 MJ/m3) and compressive strength (27.4 MPa).

Investigation of a Relative Weight Ratio of Graphite/Zinc Matrix Composite with a High-Resistance to Corrosion

There has been a significant increase in the use of composite materials to reinforce metallic structures. Such an increase has been especially noted in marine and underground applications, where there is a higher corrosion impact. Whilst there have been several attempts to investigate the mechanical properties of several synthesized composite materials, few of these have analyzed the corrosion of such composite materials at different weight ratios. The aim of this paper is to explore the best weight ratios of a graphite/Zinc composite matrix that would yield the lowest corrosion rate for a variety of applications. The research is validated using experimentation based on six additives of graphite (1wt%, 2.5wt%, 4wt%, 6wt%, 8wt%, and 10wt%), which are used as reinforcements for a range of weight ratios. The additives were prepared using the powder metallurgy method. The corrosion rate for all specimens used was carried out at the room temperature of 27 °C. Analysis results showed that 1wt% of graphite additive has the highest corrosion resistance compared to other weight ratios tested. This has been verified by examining the microstructure of the composite using an optical microscope for 12h, 24h, and 48h of immersion time in a 1M HCl acid solution.

A Study on the Wear Behaviour of Monolithic Mullite Materials for Dental Applications

The aim of this study is to evaluate the potential use of the monolithic mullite samples for the dental applications. For this purpose, at first the monolithic mullite samples obtained by the powder metallurgy method have been characterized by the scanning electron microscopy (SEM) together with the EDS analysis. The pin-on-disk tribometer has been used to conduct the wear test in order to determine the volumetric loss. After the wear tests, the worn surfaces of the sintered mullite samples have been studied. The presence of the 3Al2O3.2SiO2 structure has been confirmed by the FT-IR spectroscopy through the observation of the characteristic Al-O-Si linkages at the spectra. The wear rate results derived from the volumetric losses have been measured to be around 2.42×10-6 mm3/Nm. This value has been found to be lower than those of alumina and alumina-mullite composites in the previous studies, which explains the higher wear resistance of these mullite materials. The room temperature friction coefficients of AS-1 and AS-2 samples have been determined to be 0.88 and 0.80, respectively. The wear behaviour of the samples has been correlated to the sintering temperature and the resultant relative density of the samples. The mullite samples obtained in this study have indicated better wear performance than the other materials (alumina and alumina-mullite composites) in spite of the usage of monolithic material. Therefore, this study suggests that the monolithic mullite materials have a potential to be exploited for the replacement of the previous ceramic-based dental materials. Further studies might contribute to the improvement of these materials to be utilized in the oral environment.

TiCoCrFeMn (BCC + C14) High-Entropy Alloy Multiphase Structure Analysis Based on the Theory of Molecular Orbitals

High-entropy alloys (HEA) are a group of modern, perspective materials that have been intensively developed in recent years due to their superior properties and potential applications in many fields. The complexity of their chemical composition and the further interactions of main elements significantly inhibit the prediction of phases that may form during material processing. Thus, at the design stage of HEA fabrication, the molecular orbitals theory was proposed. In this method, the connection of the average strength of covalent bonding between the alloying elements (Bo parameter) and the average energy level of the d-orbital (parameter Md) enables for a preliminary assessment of the phase structure and the type of lattice for individual components in the formed alloy. The designed TiCoCrFeMn alloy was produced by the powder metallurgy method, preceded by mechanical alloying of the initial elementary powders and at the temperature of 1050 °C for 60 s. An ultra-fine-grained structured alloy was homogenized at 1000 °C for 1000 h. The X-ray diffraction and scanning electron microscopy analysis confirmed the correctness of the methodology proposed as the assumed phase structure consisted of the body-centered cubic (BCC) solid solution and the C14 Laves phase was obtained.

MICROSTRUCTURE AND OXIDATION BEHAVIOR OF THE OXIDE DISPERSION STRENGTHENED STAINLESS STEEL 316L WITH ZIRCONIA DISPERSION

Synthesis of the oxide dispersion sODS steels was performed by dispersing 0.5 wt % zirconia to the stainless steel SS 316L by the powder metallurgy method. The ball milling process was carried out for pre-alloying the elements continued with the consolidation performed by the compaction and sintering process using the APS (Arc Plasma Sintering). Analysis of microstructure was performed by observing the morphology, identify the phase and evaluate the oxide distribution. An oxidation test was carried out at 700oC for 8 hours using the MSB (Magnetic Suspension Balanced) apparatus to evaluate the primary oxidation curve. The same grain fineness consists of 2 dominant phases, so the presence of an austenitic phase and a ferritic phase has been analyzed from the X-Ray Diffraction pattern. The homogeneous distribution of zirconia was observed, followed by improvements in mechanical properties, which could be identified by hardness testing. The parabolic phenomenon oxidation curve was explained by the excellent high-temperature oxidation behaviour of the ODS steel, followed by the formation of ZrO2 oxide protective thin layer.