A model for calculating the metal powder pressing process with a porogen is proposed. An approximate method and algorithm have been developed that make it possible to take into account the presence of a porogen in the calculation of the pressing process and reflect all types of bonds at the contact boundaries of metal powder particles. Based on the constructed model, an approximate method and algorithm for calculating the properties of powder filter material (PFM) produced by pressing granular metal powders using a porogen have been developed. The advantage of the proposed mathematical model is the possibility of its development to describe the sintering process, as well as the possibility of its use for calculating the modified elementary cells used by researchers in modeling the structure of PFM with a porogen.
Materials Science. Non-Equilibrium Phase Transformations.
Vol. 5 (2019), Issue 4
Table of Contents
The impact of frequency composition of consolidation current on the structure and physical-mechanical properties of Ti-Al-C system metal matrix compositespg(s) 109-111
The impact of industrial frequency (50 Hz) current with the voltage of U = 10 V while using the Field Activated Pressure Assisted Synthesis (FAPAS) method as well as the impact of superposition of direct and alternating (with 10 kHz frequency) currents with the voltage of U = 2 V while using Spark Plasms Sintering (SPS) method on the phase composition, structure and properties of Ti-Al-C system metal-matrix composites, consolidated from the powder mixtures, prepared by high voltage electric discharge, is experimentally studied. It is shown, that using SPS and FAPAS methods allows synthesis of materials, dispersion-strengthened by phases of TiC and Al4C3 carbides and Ti3AlC2 MAX-phase. It is found out, that using FAPAS method allows obtainment of Ti-Al-C system composites with higher values of density, hardness and wear-resistance, than those of materials obtained by SPS due to more homogeneous structure. Such a differences can be explained by the fact that high frequency (10 kHz) current component promotes movement of disperse phase inside the matrix, which leads to the agglomeration of strengthening particles as well as to increase of obtained composite porosity up to ~ 8 %.
The use of an advanced nanotechnology coating process is absolutely helpful in immensely optimizing the efficiency of mechanical properties of materials such as: Longer service life, ability to tolerate greater loads, ease and low cost of maintenance, the environmental gain in the conservation of resources, improved response in kinetic systems, lower energy consumption, resistance to corrosion, low friction, use of low-cost base material, etc. Metal materials are usually subjected to various surface conditions that might cause stress, strain, deformation, and corrosion. Accordingly, Nano-coating technology is used to enhance the performance of mechanical properties in addition to reduce mechanical failure as much as possible. This research, a simulation of Nano coating effect on some mechanical properties performance using Finite Element Analysis (FEA) software was carried out. The prime focus here was on exposing a thin Aluminum (Al7075-T6) walled spherical vessel to internal pressure before and after coating, this spherical vessel was coated by nano- layer using two different materials such as Titanium (Ti) and Nickel (Ni) with thicknesses ranging (100 nm, 500 nm, and 900 nm). Then a comparison of the obtained results was made before and after coating, the results showed that the aluminum 7075-T6 thin walled spherical vessel was successfully coated with Titanium and Nickel separately using ANSYS software. Also the results showed that 900 nm Nickel coated aluminum 7075-T6 thin walled spherical vessel has a better improvement in mechanical properties. These improvements in mechanical properties were varied between 4.5225% to 20.724% depending on coating thickness and coating material. The Nickel coating has shown higher improvements in comparison with Titanium were observed.
Iron powder metallurgy is a method that is widely used in production of steel parts that are utilized as machine components or as parts in automotive industry. Milling is extensively used in powder metallurgy of iron, for purposes of mixing. The hardness and yield strength of milled iron powders increase due to work hardening. This leads to low green density of the cold pressed green parts, prior to sintering. In powder metallurgy, warm compaction is utilized for enhancing the green density and green strength.
In the present study, effect of warm compaction of milled iron powders was investigated. For warm compaction of iron powders, 600 MPa pressure was applied in a steel die at 150 oC. The microstructure of the milled samples was examined by scanning electron microscopy. Hardness values of the cold pressed and warm compacted samples were determined by a Brinell hardness tester. Bending strength values of the samples were determined by a universal testing machine. It was found that the hardness of the cold compacted green samples increased considerably, from about 40 Brinell10 to about 140 Brinell10, as a result of warm compaction. Bending strength values increased to over 100 MPa after warm compaction; whereas the bending strength of the cold compacted green samples were in 10-20 MPa range.
Features of structure, phase composition and properties of hotforged high-entropy alloys of Ti-Cr-Fe-Ni-C systempg(s) 123-126
Powder high-entropy alloys (HEA) of TiCrFeNiC equioatomic composition were synthesized by hot forging (HF). The phase composition and parameters of the fine structure of the alloys are determined. It is shown that at all annealing temperatures of the alloys their phase composition does not change significantly and consists of two solid solutions of substitution – FCC and BCC and two carbide phases – TiC and Cr3C2. The mechanical properties of the alloys are at a rather high level – so the maximum strength of the alloy was 2243 MPa and the hardness is more than 62 HRC, which can be explained by the effect of high entropy and in situ synthesis of carbides in the manufacture of alloys.
The MAX-phase Ti3AlC2 was synthesized by sintering method. The study of sorption properties of the sample was carried out under conditions continuous heating. It was established that desorption of hydrogen begins at a temperature of ~ 210 °С. After complete desorption, the sample was re-heated in an atmosphere of hydrogen. It was found that Mg-5 wt% Ti3AlC2 composite begins absorb hydrogen at a temperature of ~ 76 °С. As a result of cycling, the temperature of desorption has shifted towards lower values ~ 186 °C.
Melting and crystallization of heterophase non-metallic inclusions ―eutectics‖ was investigated. Mechanism of melting of the eutectic inclusions and inclusion-matrix boundaries under contact laser melting with steel matrix in the conditions of abnormal mass transfer connecting with formation of zones with high dislocation density and also with electron and electro-magnetic interaction between inclusion and steel matrix was proposed. That allows to create the possibilities for the influence on the inclusion-matrix boundaries and also on the chemical and phase composition of surface layer of non-metallic inclusions. Peculiarities of structure of non-metallic inclusions after speed crystallization were investigated. It was shown that under laser action the initial composite colonial structure of inclusions transits into abnormal eutectic structure. Also it was shown that under laser action the initial structure of inclusion-steel matrix boundaries transits into unstable equilibrium high-energy condition that cause development of the dissipation processes connecting with aspiration of system inclusion-matrix to the state with minimum of the free energy. In the result of the system eutectic inclusion-matrix transits to the state of unstable equilibrium which determines structure and properties of laser-quenched interphase boundary. Processes of melting, fusion and dissolution of non-metallic inclusions ―eutectics‖ and also of the melting of steel matrix play the great role in transformation of interphase inclusion-matrix boundaries under laser action.
Sn-Ag powder alloy of eutectic composition is demanded in the production of powders for soldering pastes used in electronics. Non-eutectic alloy has found its application in catalysis for CO2 reduction, in 3D printing, as the promising material for lithium ion batteries. In this work the way of synthesis of Sn–Ag nanostructured powder alloy with near-eutectic composition based of cementation reaction in the system Sn0/Ag+ in aqueous solutions was proposed. The peculiarities of alloy powder synthesis in acid and slightly acid solutions were studied. Factors influencing on powder microstructure, phase and elemental composition were identified. Electrochemical behavior of tin in aqueous solutions for silver deposition was studied by potentiometric method.
A theoretical study of the process destruction of a solid surface under the action of a powerful radiation impulse is carried out. The peculiarities of the dynamics the surface destruction of the material and the features of the space-time dynamics of the gaseous phase were studied. This phase occurs as a result of local phase changes on the surface of the irradiated material. The differential equation to describe the dynamics of the corrosion crater formation on a solid surface was researched. This equation is analyzed together with equation of near-surface pressure dynamics. The asymptotic analysis for crater equation gives the basis to assert that mathematical interpretation of process of destruction corresponds to actual temporal dynamics of formation of a crater on the substance. The numerical simulation of the formation of a nanocrater with a model form of an active laser impulse is given. The test calculations correspond to experimental observation and theoretical ideas about the process of development of a corrosion crater under laser pulsed irradiation.
Using innovative technology, high alumina corundum ceramic products for ballistic protection have been produced and their elastic, physical and mechanical characteristics have been tested. The products are of different shape and thickness and are applied in the construction of the front layer of macro-dispersed ceramic-polymer modular systems for individual protection and for armoring of aircraft, of water and land mobile and stationary military objects, and the like.