International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

The article investigates the influence of technology and technological parameters of manufacturing on the structure, phase composition and physical and mechanical properties of the Fe-FeCr800 composite system. It was established that the determining factor in phase and structure formation is the manufacturing technology, while vacuum sintering and hot forging have their own optimal technological parameters. At the same time, hot forging makes it possible to obtain a composite with a higher microhardness of structural components due to a change in the content of component components. The results of the research also showed that the preheating time (for 20 min.), as well as thermomechanical treatment, is sufficient for the phase formation process, in particular, with the release of carboboride phases of the type Me3CB and Me3(CB)2, while the densification processes are intensified, which makes it possible to obtain a material with lower residual porosity. Analysis of mechanical tests showed that vacuum sintering makes it possible to obtain composites with higher mechanical properties due to the active interaction between the components of the composite. However, high-temperature annealing after hot deformation will allow for a composite with high mechanical properties.

An experimental study was carried out to develop a technique for manufacturing a high silicon Al-Si-Ni sintered alloy with a coefficient of thermal expansion close to steels. A stage of hot forging was added to overcome porosity and improve silicon inclusions morphology to obtain better mechanical properties. Liquid and solid phase regimes of sintering were studied for the material made of the elemental components powders mixture as well as of a pre-alloyed powder. The impracticality of liquid-phase sintering modes is shown for this type of material primarily because of the tendency to liquid-phase exudation. It was proposed to carry out a solid-state vacuum sintering with subsequent hot deformation. Only the pre-alloyed powder is suitable for the technique; the other way, it leads to the course and sometimes, not equilibrium intermetallic inclusions will form in place of nickel particles because of the insolubility of Ni in solid Al. It is shown the possibility of successful plastic deformation of this material after sintering despite its extremely low ductility, which helps successfully overcome porosity and improve the characteristics of the microstructure of the material.

Mechanical tests of 5- and 6-component high-entropy alloys, which were obtained for the first time by the method of hot forging, were carried out. The test results showed a fairly high hardness and strength of the obtained alloys. The TiCrFeNiC alloy (without annealing) has the highest mechanical properties. Its high strength is due to solid-solution hardening, as well as the formation of carbides in situ. Fractographic studies showed mostly quasi-brittle destruction of alloy samples.

The peculiarities of the structure and phase composition of the high-entropy alloy of the TiCrFeMnSiC system obtained from the powder mixture of ferrotitanium, ferrochrome and ferrosilicon-manganese ferroalloys are considered in the work. The technological scheme of alloy production included joint grinding of the mixture in a planetary mill, consolidation of the blanks, their heating to 1100 0C, hot forging on the arc press and subsequent annealing of hot-forged samples at 1200 0C. According to the results of X-ray analysis of the obtained alloy, it was found that the main phase of the alloy is the BCC phase with the parameter of the cubic lattice a = 0.2868 nm, which is a solid solution based on alloying components of the original charge. The phase composition of the composite also recorded ti tanium carbide TiC with FCC lattice with the parameter a = 0.4319 nm, which corresponds to a stoichiometric composition of about TiC0.6 and a small amount of FCC phase of iron-chromium carbide (Cr, Fe)23C6 with lattice parameter a = 1.0645 nm. The material has a high hardness (up to 60-61 HRC), which can provide high resistance of this multicomponent alloy.

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.

Equiatomic alloys TiCrFeNiCuC were made by two methods of powder metallurgy – vacuum sintering and hot forging followed by annealing. In the process of sintering the TiCrFeNiCuC blanks, the influence of entropy of mixing resulted in the formation of solid substitution solutions mainly on the basis of the FCC lattice, and also formed titanium carbide (TiC0.74). In samples obtained by hot forging and subsequent annealing, two carbides TiC and Cr3C2 were found, and titanium carbide being formed with lower carbon content (TiC0.58). In addition, the forged samples showed significantly higher values of the defect of the crystalline structure, which leads to increase in their hardness.

The results of the estimation for the influence of titanium diboride content in the initial powder mixture on the basic mechanical properties at the tests on tension and compression are presented. It is shown that the porosity of sintered at 1250 0C preforms from TiH2-TiB2 powder mixture increases with increasing of titanium diboride content in the initial charge, which is due to the manifestation of the Frenkel effect at sintering. The values of tensile strength, hardness and elastic modulus, despite some porosity growth of the sintered alloy, increase with the addition of 5 % of TiB2 powder, while increasing the content of the high modulus component in the mixture to 10 % leads to decrease in the level of these characteristics. The plasticity of sintered alloys monotonically decreases with increasing of the boride component content. At compression tests, the yield point and the compressive strength increase monotonically with increase in TiB2 content, despite the increase in porosity of the latter, due to a significantly lower effect of porosity on the value of the resistance to deformation in compression compared with tension. The use of hot forging of sintered powder preforms leads to increase of strength properties and hardness of the composites.

The possibilities of Fe-Al intermetallic system production by vacuum sintering and impact consolidation of powder bodies, as well as the influence of the regimes of the methods used on the structure and properties of iron aluminides were studied in the article. Mixture of iron and aluminum powders were used for fabrication of iron aluminide Fe₃Al. The powder samples were compacted and vacuum sintered at temperatures of 1250, 1350, 1400 and 1450 °C, and also using hot forging at a temperature of 1050 °C and 1150 °C. It is shown, that the increase of density is observed only at a temperature of 1400 °C. At sintering temperature of 1450 °C the samples reach a density of 6,35 g/cm³, which is 94% of the theoretical value. Only the use of hot forging makes it possible to obtain nonporous samples. It is shown, that bending strength, fracture toughness and hardness increase with increase of sintering temperature, but higher values of this parameters have the samples, produced with use of hot forging.

The effect of metal phase composition in the Fe-based + (2 % glass) powdered composites on the basic mechanical and tribological properties of the composites, made by means of sintering and hot forging, have been investigated. As a basis for the metallic phase of the composite the mixtures of iron powders with additives of graphite, B₄C, BN and Cu at different ratio were used. It was shown that at sintering of metal-glass material the reaction of glass phase with oxides on the surface of iron powder particles takes place, resulting in a change of glass phase chemical composition. The results of materials mechanical properties investigations had shown that the highest strength properties and hardness have the composites with the content of the initial powder mixture of 5% Cu and 2% B₄C, while the best tribological properties have the composites with 2% B₄C, 5% Cu and 1% BN.

The results of investigations of the structure and the elastic characteristics of the aluminum-matrix composites of Al-TiC system, produced by hot forging in accordance with different technological schemes are presented. It is shown that the materials obtained by hot forging differ in appreciable anisotropy, which is characterized by the elongation of the particles of the matrix phase in the direction normal to forging force. Hereupon the resulting values of both normal elasticity modulus and shear modulus in the plane normal to the direction of the deforming force during hot forging, are of 12-15% higher than the corresponding characteristics in the direction of deformation. For all of the above manufacturing processes the elastic characteristics of the investigated aluminum-matrix composites exceed by 40-70% (depending on the direction of sounding) the Young modulus of aluminum, and the respective characteristics of the shear modulus are higher by 8-15%.

Aluminum matrix composites composed of Al, Al-5,6 wt.% Cu (Al5.6Cu), Al-7 wt.% of alpha brass α-Cu_0,8Zn_0,2 (Al7CuZn) and Al-9 wt.% of nickel brass Cu_0,64Zn_0,31Ni_0,05 (Al9CuZnNi) as the matrix and 15 vol.% of TiC and synthesized Al-Ti-C master alloy (MA) as the reinforcement were successfully fabricated by hot forging. Sliding wear tests were conducted at different velocity and loads using a pin- on-disc apparatus and under dry conditions. The results of the investigations indicate that the coefficient of friction significantly lower in composites with Al-Ti-C master alloy then that reinforced with TiC, while the wear rates are lower in composites with Cu additions. The post-test analysis of the material damage mechanisms were examined by optical profilometer.

The capabilities of powder hot forging for manufacturing of Fe₃Al intermetallics and effect of forging and following thermal treatment routines on their structure and properties had been investigated. Fe₃Al intermetallic powders were produced by means of thermal synthesis at 1000°С in vacuum from a mixture of Fe and Al elemental powders. Hot forging of consolidated preforms had been carried out from 1000, 1050, 1100 and 1150°С and afterwards the hot forged preforms were subjected to supplementary sintering in vacuum at 1100÷1450°С. It is foud, that thermal synthesis of Fe + 14% Al powder mixture results in formation of Fe₃Al phase. Sintering of hot forged specimens result in increasing of strength and crack growth resistance, which values enhance with increasing of sintering temperature. Otherwise the hardness of hot forged intermetallics decreases after their sintering. The influence of modes of treatment on the structure and properties of the materials was investigated. It has been established that the strength and fracture toughness of the intermetallics obtained from milled blend after hot forging had the higher values as compared with the alloy made from the batch without its milling.