Microhardness Of Surface Layer Research Articles

Evolution mechanism of microstructure and microhardness of Ti–6Al–4V alloy during ultrasonic elliptical vibration assisted ultra-precise cutting

The ultra-precision Ti–6Al–4V alloy parts are growing used in medical and aerospace industries, and which always work in the extreme working conditions such as high temperature, high pressure, and variable load. Thus, the requirements for machining accuracy and surface quality of parts are getting higher and higher. The ultrasonic elliptical vibration assisted cutting (UEVC) technology has been proved to be an effective method for the ultra-precision machining of Ti–6Al–4V alloy. However, in the UEVC process, the evolution mechanism of microstructure and microhardness, which directly affect the service performance and life, is unrevealed. In this paper, the comprehensive investigations of microstructural plastic deformation, grain refinement, phase transformation and microhardness of machined surface layer under conventional cutting (CC) and UEVC processes are carried out. The experimental results indicated that, due to the effects of UEVC technology, the plastic deformation area show obvious compression deformation, the depth of plastic deformation is less than 10 μm, there is no obvious phase transformation on the machined surface layer material, and the hardening rate of machined surface is more than 20%. These findings show the UEVC technology has a unique influence on the microstructure and microhardness of Ti–6Al–4V alloy, which have important implications for the cutting parameter design of ultra-precision Ti–6Al–4V alloy parts.

Effect of laser shock peening on surface integrity and tensile fatigue behavior of TB8 bolts

Laser shock peening (LSP) treatment was introduced to improve tensile fatigue behavior of TB8 titanium alloy bolt. TB8 bolts surface integrity, tensile fatigue fracture and strengthening mechanism after LSP treatment were systematically investigated. Results showed that cracks and machining defects on the thread surface were eliminated, surface layer microhardness and compressive residual stress were increased after LSP treatment. Meanwhile, the grains sizes of the LSP treated bolts samples were reduced to 38.61 μm with the formation of high density dislocations. LSP treated bolts samples with 80 mJ laser energy exhibited the maximum average tensile fatigue life, which was increased from 66,452 cycles to 81,319 cycles. In addition, under the synergistic effect of compressive residual stress and grains refinement, cracks propagation path was changed, which were the primary factors for the improvement of TB8 bolt tensile fatigue life.

Analysis of Geometric Surface Structure and Surface Layer Microhardness of Ti6Al4V Titanium Alloy after Vibratory Shot Peening.

This article presents an analysis of the impact of vibratory shot peening on the surface roughness and physical properties of the Ti6Al4V titanium alloy surface layer after milling. The elements of machine parts and structures made of titanium alloys are often exposed to variable loads during operation. Therefore, it is advisable to apply methods that enhance functional properties and increase the durability of interacting components. Increasing the operational durability of such elements can be achieved by vibratory shot peening. Variable amplitudes A = 24; 33; 42; 51; 60 mm and times t = 1; 7; 13; 19; 25 min were applied. It has been demonstrated that it is possible to achieve a threefold reduction in the roughness parameter, Sa = 0.344 µm, compared with milling, Sa = 0.95 µm. An increase in Smr(c) areal material ratio was observed after vibratory shot peening compared with milling. It has been shown that amplitude has a greater impact on the increase in hardening of the surface layer gh compared with time. The highest rate of change in surface roughness and thickness of the hardened layer was achieved at a vibratory shot-peening time of t = 13 min. The greatest thickness of the hardened layer, exceeding 200 µm, was obtained after shot peening with an amplitude of A = 60 mm.

Finite Element Simulation and Experimental Investigation of Nanostructuring Burnishing AISI 52100 Steel Using an Inclined Flat Cylindrical Tool

This article is devoted to the development of a sliding burnishing scheme using a flat cylindrical indenter. The previously established patterns of nanostructured state formation in the AISI 52100 steel subsurface layer showed a need to create a special tool with a variable tilt angle of the indenter and with force regulation. A new tool with a cubic boron nitride indenter opens wide possibilities for nanostructuring burnishing of hardened bearing steel. Firstly, a flat cylindrical indenter has high durability due to repeated rotation around its axis. Secondly, the change of the tilt angle to the treated surface allows controlling the contact compression pressure and plastic shear deformation, which determines the formation of a nanostructured state of the material by the method of severe plastic deformation (SPD). The purpose of the work is to determine the optimal parameters of the process and tool in order to form a nanostructure and significantly increase surface layer microhardness. The goal was achieved by the methods of finite element modeling (FEM) and experimental studies of burnishing when the indenter tilt angle changes from 0.5° to 2.5° under dry processing conditions. Numerical simulation of the process made it possible to establish optimal values of the indenter tilt angle of 2° and the burnishing force 250 N according to the criteria of maximum contact pressure and cumulative deformation. The experimental studies of cumulative deformations and the coefficient of friction by the method of burnishing a split disc and dynamometry of the process confirmed the FEM results. The transmission microscopy, durometry, and 3D surface profilometry showed the sensitivity of nanocrystallite sizes, microhardness, and roughness to an indenter tilt angle and confirmed the optimality of the established tilt angle value.

Термическая стабильность структурно-фазового состояния алюминия и сплавов системы Al – Si, легированных атомами циркония при воздействии компрессионных плазменных потоков

The results of structural-phase state investigations of Аl, Al – 12,6 wt. % Si – 0,1 wt. % Fe and Al – 12,6 wt. % Si – 0,5 wt. % Cu – 2,7 wt. % Mg – 0,3 wt. % Ni – 0,3 wt. % Fe – 0,2 wt. % Mn alloys surface layers alloyed by zirconium atoms under action of compression plasma flows are presented. The formation of metastable compounds Al3Zr with L12 structure and (Al,Si)3Zr with D022 structure in the alloyed layers of aluminum and silumin samples, respectively, was found. Alloying with zirconium atoms makes it possible to increase the microhardness of surface layer in 1.4 – 3 times. Thermal stability of the structure and phase composition of alloyed layers at 550 °C was investigated. The transformation of Al3Zr – L12 into Al3Zr – D023 phase in aluminium and (Al,Si)3Zr disintegration with ZrSi2 in Al – Si alloys was observed during annealing. The formed surface layers had elevated temperature strength.

Effective combined surface hardening processes of structural steels using ultrasound

The effectiveness of hardening of the surface layer of machine parts is evaluated by the operational properties of the surface layer and depends on many conditions that characterize the specific features of the technological process in which this method of hardening is carried out. The surface plastic deformation of structural steels with the use of ultrasound is studied. Four variants of hardening are considered: ultrasonic treatment with continuous supply of ultrasonic energy, pulse ultrasonic treatment, combination of ultrasonic treatment with subsequent pulse treatment, ultrasonic treatment after hardening with induction heating. It is shown that ultrasonic treatment increases microhardness of surface layer of structural steels by 1.5 times, HF hardening by more than 2 times, HF hardening + UZO combination by 3 times and HF hardening + IUZO combination by 3.2 times. Ultrasonic treatment increases compression stresses occurring in steel surface hardened by HFI hardening. The compressive stresses increase especially strongly after pulse ultrasonic treatment with five passes and reach the value of 1200 Pa.

STRENGTHENING OF PIPE-PRESSING TOOLS FOR THE PRODUCTION OF CORROSION-RESISTANT PIPES USING CHEMICAL AND THERMAL TREATMENT

Problem statement. In the production of corrosion-resistant pipes at pipe-pressing plants, the low durability of the pipe tool is a burning issue. High mechanical properties of the tool and its heat resistance (redness resistance) are achieved due to alloying and heat treatment. However, the “traditional” means of increasing wear resistance (hardening with tempering, thermomechanical processing) are almost exhausted. Therefore it is of some interest to develop and correct thermal and chemical-thermal treatment methods in order to increase the wear resistance of the tool. Chemical and thermal treatment is an effective way of changing the surface layer composition for a stamping tool to provide the necessary set of properties for its working surface. This changes the structure and properties of the surface layer and increases the strength, wear and heat resistance of the steel through the formation of carbides, nitrides, borides, etc. that are stable during heating process. Conducting carbonitridation in melts of cyanate salts and carbonates for matrix rings of complex matrices and mandrel needles for pressing pipes on pipe profile presses significantly increases the durability of the tool due to high indicators of surface hardness, fatigue strength by 50…60 % due to the creation of compressive stresses on the surface; improves the surface quality of the tool itself and, as a result, the quality of corrosion-resistant pipes inner surface. Ionic nitriding (compared to furnace nitriding) has the following advantages: it accelerates diffusion processes by 1,5−2 times; allows to get a diffusion layer of adjustable composition and structure; characterized by slight deformations of products and a high class of surface cleanliness. The purpose of the article – to show the expediency of using modern chemical-thermal treatment technologies (carbonitridation, ionic nitriding), which increase the hardness and wear resistance of the tool, which ensures the quality of corrosion-resistant pipes inner surface and reduces the costs of processing the pipes manufacture, as well as the effectiveness of building a mathematical model of the distribution of microhardness in surface layers of the tool after chemical and thermal treatment with the help of applied computer programs “MathCad”, “Excel”. Conclusions. Due to the low durability of the pipe press tool, there was a need to improve the strengthening technologies of the pipe tool, optimize the modes of such technologies, and develop new strengthening methods. Conducting chemical-thermal treatment after hardening and tempering of tool steel Х40CrMoV5-1-1and 30WCrV17-2 (carbonitridation, ion nitriding) significantly increases the operational properties of the tool and its service life by 25…30 %, as well as the quality of its surface, which significantly increases the quality of corrosion-resistant pipes inner surface.

Influence of Slide Burnishing Parameters on the Surface Layer Properties of Stainless Steel and Mean Positron Lifetime.

This paper presents the results of an experimental study on the impact of slide burnishing on surface roughness parameters (Sa, Sz, Sp, Sv, Ssk, and Sku), topography, surface layer microhardness, residual stress, and mean positron lifetime (τmean). In the study, specimens of X6CrNiTi18 stainless steel were subjected to slide burnishing. The experimental variables were feed and slide burnishing force. The slide burnishing process led to changes in the surface structure and residual stress distribution and increased the surface layer microhardness. After slide burnishing, the analyzed roughness parameters decreased compared with their pre-treatment (grinding) values. The slide burnishing of X6CrNiTi18 steel specimens increased their degree of strengthening e from 8.77% to 42.74%, while the hardened layer thickness gh increased after the treatment from about 10 µm to 100 µm. The maximum compressive residual stress was about 450 MPa, and the maximum depth of compressive residual stresses was gσ = 1.1 mm. The positron mean lifetime τmean slightly yet systematically increased with the increase in burnishing force F, while an increase in feed led to changes of a different nature.

Study on the Surface Layer Properties and Fatigue Life of a Workpiece Machined by Centrifugal Shot Peening and Burnishing

This paper presents the results of research on the impact of finishing method on surface topography, surface roughness (parameters Ra, Rt, Rpk, Rk, Rvk), surface layer microhardness, residual stresses and fatigue life. Ring samples made of C45 steel were used to conduct the experiments. The following finishing machining methods were selected: slide burnishing, ball burnishing, centrifugal shot peening, centrifugal shot peening + slide burnishing and centrifugal shot peening + ball burnishing. In the first stage, the use of combined shot peening + burnishing enables microhardness to be increased on the surface layer, the values of residual stresses to be increased and the creation of characteristic machining traces on the surface, the so-called “dimples” (effect of centrifugal shot peening). On the other hand, burnishing (slide burnishing or ball burnishing) is aimed at smoothing the surface and providing favorable stereometric properties to the surface layer. It was noted that, after finishing, the surface roughness parameters decreased from 59% to 83% in relation to the reference surface. The exception is the centrifugal shot peening technology. The use of burnishing (slide or ball burnishing) after centrifugal shot peening reduces the surface roughness parameters by a maximum of 82% compared to the value after centrifugal shot peening. The highest increase in microhardness was obtained after centrifugal shot peening + slide burnishing (ΔHV = 105 HV 0.05), while the highest thickness gh (gh = 120 μm) was obtained after centrifugal shot peening + ball burnishing. The combination of centrifugal shot peening and ball burnishing results in the highest absolute value of compressive residual stresses σmax = 602 MPa and depth gσ = 0.41 mm). Application of an additional operation after centrifugal shot peening increases fatigue life from 27% to 49%. ANOVA analysis of variance confirms the significance of the processing effect of centrifugal shot peening combined with slide burnishing (CSP + SB) and centrifugal shot peening + ball burnishing (CSP + BB) on the analyzed dependent surface.

Features of formation of diffusion zone obtained on steel 20 by boriding in induction furnace

The article presents data on studies of iron borides synthesis during induction heating to 1000 °C for 5 min of steel 20 samples with a coating from a charge containing Fe – H3BO3. Content of boric acid in the charge varied from 25 to 75 % wt. Charge in the experiments could be diluted with a solution of liquid glass in water with addition of small amount of ammonium hydroxide and coal. Study of the surface layer microhardness showed that during saturation of the surface layer of carbon steel 20 with boron, a macroscopically extensive diffusion zone 900 – 1000 μm in size is formed, in which the boride content gradually decreases when moving deeper into the matrix. Such a size of the diffusion zone indicates an anomalously high mass transfer during boriding of steel 20. Indeed, the calculated diffusion coefficient during boriding under induction conditions (about 1.35·10–9 m2/s) is two orders of magnitude higher than the diffusion coefficient in the classical boriding. X-ray studies showed that, under the considered conditions, Fe2B and FeB borides are synthesized, and a solid solution of boron in α­iron is also formed. An analysis of phase composition of the diffusion zone structural components indicates that, from the surface to the matrix, formation of boride phases occurs in the following sequence: FeB → Fe2B → (α­phase + B) → base metal. Microstructure of the diffusion zone consists of more or less pronounced layers consisting of FeB and Fe2B boride phases. On the whole, especially deep-ying regions of the diffusion zone are a composite material consisting of plastic α-phase and iron boride crystals. Crystals in FeB and Fe2B in the layer are oriented mainly perpendicular to the diffusion front. Perhaps, this is due to the rapid predominant growth of the boride phase under conditions of high diffusion mobility of boron atoms in one direction and hindered in others.

The Influence of the Depth of Grinding on the Condition of the Surface Layer of 20MnCr5 Steel Ground with the Minimum Quantity Lubrication (MQL) Method.

This paper describes the research on abrasive machining conditions and their influence on microhardness and residual stresses distribution in the technological surface layer of 20MnCr5 steel. The roughness of ground samples was also measured. Samples underwent a vacuum carburizing process (LPC) followed by high-pressure gas quenching (HPGQ) in a 4D quenching chamber. Processes were realized with a single-piece flow method. Then, the flat surfaces of samples were ground with a Vortex type IPA60EH20VTX alumina grinding wheel using a flat-surface grinder. The samples were ground to three depths of grinding (ae = 0.01; 0.02; 0.03 mm) with grinding fluid supply using either flood method (WET) or minimum quantity lubrication (MQL) method. The condition of the technological surface layer was described using microhardness and residual stresses, as well as some selected parameters of surface roughness. The results obtained revealed that changes in microhardness as compared to microhardness of the material before grinding were lower in samples ground with grinding fluid supplied with MQL method. At the same time, the values of residual stresses were also better for samples ground using MQL method. Furthermore, the use of grinding fluid fed with MQL method produced lower values of surface roughness compared to the parameters obtained with WET method. It was concluded that for the tested scope of machining conditions, the MQL method can be a favourable alternative to the flood method of supplying grinding fluid into the grinding zone.

Сравнительный анализ изменения структуры и свойств сплавов системы Al–Si, подвергнутых электровзрывному легированию

The paper presents the comparative analysis of the structure and mechanical properties (microhardness) of the surface layers of the hypoeutectic Al–11Si alloy and hypereutectic Al–20Si alloy exposed to electroexplosive alloying (treatment mode: aluminum foil mass is 58.9 mg; Y2O3 powder mass is 88.3 mg; the discharge voltage is 2.6 kV). During the research, the authors identified that the Al–11Si alloy initial structure mainly consists of the Al solid solution grains. Eutectic grains are located along the grain boundaries and at the joints of aluminum grain boundaries. In the Al–11Si alloy, the aluminum grain size varies from 25 μm to 100 μm, and the Al–Si eutectic grain size varies within 10–30 μm. The hypereutectic composition Al–20Si alloy in the initial state is characterized by the presence of primary silicon inclusions predominantly of a plate-like shape. The sizes of these inclusions reach 120 μm. After electroexplosive alloying, in the Al–11Si alloy, the author identified the formation of a multilayer structure consisting of a highly-porous coating irregular in thickness, a liquid-phase alloying layer, and a heat-affected layer. The modified layer thickness for the Al–11Si alloy varies in the range of 33–60 μm, and for the Al–20Si alloy, the modified layer thickness varies within 20–100 μm. The microhardness value of the initial hypoeutectic Al–11Si alloy was 64 HV 0.05, for the hypereutectic Al–20Si alloy – 71 HV 0.05. It can be noted that the microhardness of the Al–11Si alloy surface layer exceeds the initial material microhardness more than 2.5 times. In the Al–20Si alloy, the surface layer microhardness exceeds the one of the initial material more than twice. With the increase of the distance from the modification surface, the microhardness decreases and reaches the initial alloy value at the depth of ≈90 μm.

Effect of electron beam treatment on the structure and properties of AlCoCrFeNi high-entropy alloy

In the last decade the attention of scientists in the field of physical material science has been drawn to the study of high entropy alloys. Using wire arc additive manufacturing (WAAM) technology the high-entropy alloy (HEA) AlCoCrFeNi of nonequiatomic composition has been produced (wt. %: 15.64 Al; 7.78 Co; 8.87 Cr; 22.31 Fe; 44.57 Ni). It is shown by methods of modern material science that the HEA is a polycrystalline material with a grain size 4–15 μm along whose grain boundaries the second-phase particles are detected. It is shown by the mapping methods that bulks of grains are enriched in aluminium and nickel while grain boundaries contain chromium and iron. Cobalt is quasi-uniformly distributed in crystal lattice of the manufactured HEA. The material ultimate strength in testing for compression depends on production mode and varies within the interval from 1300 to 1800 MPa. The HEA wear parameter amounts to 1.4∙10−4 mm3/N⋅m, friction coefficient — 0.65. In testings for tension the material failure occurred by the mechanism of intragrain cleavage. The formation of brittle cracks along boundaries and in grain boundary junctions i.e. in sites containing the inclusions of second phases is revealed. One of the reasons of HEA increased brittleness is the revealed nonuniform distribution of elements in alloy structure. The HEA’s irradiation by pulsed electron beam with energy density of 10–30 J/cm2 (pulse duration 200 μs, number of pulses 3) results in material homogenization. High-velocity crystallization of molten surface layer of HEA samples is accompanied by the formation of columnar structure having a submicro-nanocrystalline structure. The HEA irradiation results in the increase in hardness and plasticity of the material. The largest increase (1.6 times) in ultimate strength is obtained in the alloy after electron beam processing with energy density of 30 J/cm2. Electron beam processing leads to decrease in microhardness of alloy surface layer up to 90 μm thick. The research was supported by Russian Research Foundation grant (RSF) (project № 20-19-00452).

Analysis of Surface Properties of Nickel Alloy Elements Exposed to Impulse Shot Peening with the Use of Positron Annihilation.

The paper presents the results of experimental studies on the impact of impulse shot peening parameters on surface roughness (Sa, Sz, Sp, Sv), surface layer microhardness, and the mean positron lifetime (τmean). In the study, samples made of the Inconel 718 nickel alloy were subjected to impulse shot peening on an originally designed stand. The variable factors of the experiment included the impact energy, the diameter of the peening element, and the number of impacts per unit area. The impulse shot peening resulted in changes in the surface structure and an increase in surface layer microhardness. After the application of impulse shot peening, the analyzed roughness parameters increased in relation to post-milling values. An increase in microhardness was obtained, i.e., from 27 HV 0.05 to 108 HV 0.05 at the surface, while the maximum increase the microhardness occur at the depth from 0.04 mm to 0.08 mm. The changes in the physical properties of the surface layer were accompanied by an increase in the mean positron lifetime τmean. This is probably related to the increased positron annihilation in point defects. In the case of small surface deformations, the increase in microhardness was accompanied by a much lower increase in τmean, which may indicate a different course of changes in the defect structure consisting mainly in modification of the dislocation system. The dependent variables were subjected to ANOVA analysis of variance (it was one-factor analysis), and the effect of independent variables was evaluated using post-hoc tests (Tukey test).

Distributions of grains and precipitates in gradient lamellae Al–Zn–Mg–Cu alloy by ultrasonic surface rolling processing

Improving surface properties can effectively expand the industrial application of aluminum alloys. In this study, a gradient nanostructured surface layer was successfully fabricated in an aged Al–Zn–Mg–Cu alloy by ultrasonic surface rolling processing (USRP). The microstructure and microhardness of the gradient nanostructured surface layer were investigated. The results show that a perfect gradient lamellae structure was fabricated in the surface layer. The average structural size in the topmost surface layer is approximately 41 nm, and the depth of nanostructure lamellae layer is up to 50 μm. After the USRP and two years of natural aging, the gradient distribution of precipitates was formed in gradient lamellae structure. A large number of discontinuous coarse η phase are formed on the lamellae boundary throughout the lamellae structure. However, the precipitates inside the lamellae have gradient distribution. The volume fractions of precipitates increase gradually from nanostructure to ultrafine-grained structure, and the main precipitates are GPII zones. The microhardness in the topmost surface is increased by 40% and gradually decreases from the surface to the matrix. The increase in microhardness is attributed to the fact that the enhancement of the hardness by the grain refinement is greater than the decrease due to the reduction of the precipitates inside the gradient lamellae structure from the surface to the matrix. This study provides technical method and theoretical basis for improving the surface hardness of Al–Zn–Mg–Cu alloy.

Effect of Surface Micro-Hardness Change in Multistep Machining on Friction and Wear Characteristics of Titanium Alloy

The machined surface quality, especially the micro-hardness of machined surface layers, is strongly correlated to the friction and wear characteristics of titanium alloy engineering parts. Therefore, to explore relationship of the local surface micro-hardness change in multistep machining and the surface wear resistance of the machined parts is urgently necessary. The machined surfaces were acquired through two-step (roughing and finishing) and three step (roughing, semi-finishing, and finishing) cylindrical turning experiments. The dry friction and wear tests were carried out by UMT-2 friction and wear tester on the multistep final machined surface along the feed direction. The surface wear microtopography and subsurface microstructure were observed and analyzed by scanning electron microscope. The micro-hardness variation in the local area of the finishing surface will cause the extension of unstable friction time stage while withstanding the cyclic and alternating contact stresses, and the soft–hard alternating area should be the sources of friction and wear defects, for instance cracks, peeling pits, fracture striations and even the wear fracture zone to crack propagation and peeling off. This will be of great significance to accurately control the machined surface quality and adaptively improve the surface wear resistance of titanium alloy components.

ВЛИЯНИЕ МАТЕРИАЛА И РАЗМЕРОВ ИЗДЕЛИЯ НА ПАРАМЕТРЫ УПРОЧНЕНИЯ ВОЛНОЙ ДЕФОРМАЦИИ

Previously it was defined that geometrical dimensions of material worked have a significant impact upon the process of wave deformation strengthening, as at equal volumes of strengthened samples and processing modes there are observed different cards of micro-hardness in surface layers. 
 In the paper there are shown investigations of the impact of dimensions of samples made of different material kinds (steel 45, titanium VT 1-0, bronze BRAZh 9-4, aluminum alloy B-95) upon wave deformation strengthening parameters). The investigations mentioned were carried out for the first time on a test desk specially developed. Strengthening effectiveness was estimated according to micro-hardness distribution in a surface layer. The analysis of the results obtained allowed defining that in chosen modes of WDS takes place strengthening not only a face surface but a back one of the sample at that in the core of the sample an initial hardness of material is kept. The investigations carried out allowed defining the fact that at the increase of material thickness from 10 to 20 mm resulted in the growth of degree (ΔHμ) and depth (hμ) of strengthening at WDS of samples of steel 45 - by 24 and 32%, samples of bronze BRAZh 9-4 – by 22 and 21%, samples of titanium VT 1-0 – by 24 and 32%, samples of aluminum alloy B-95 – by 40 and 62%. The samples length increase from 50 to 100 mm is accompanied by the decrease of ΔHμ and hμ at strengthening: steel 45 – by 36 and 70%, bronze BRAZh 9-4 – by 27 and 43%, titanium VT 1-0 – by 24 and 32%, aluminum alloy B-95 – by 40 and 62%.

Advanced Complex Analysis of the Thermal Softening of Nitrided Layers in Tools during Hot Die Forging.

This article is devoted to the issues of thermal softening of materials in the surface layer of forging tools. The research covers numerical modeling of the forging process, laboratory tests of tempering of nitrided layers, and the analysis of tempering of the surface layer of tools in the actual forging process. Numerical modeling was supported by measuring the temperature inside the tools with a thermocouple inserted into the tool to measure the temperature as close to the surface as possible. The modeling results confirmed the possibility of tempering the die material. The results of laboratory tests made it possible to determine the influence of temperature on tempering at different surface layer depths. Numerical analysis and measurement of surface layer microhardness of tools revealed the destructive effect of temperature during forging on the tempering of the nitrided layer and on the material layers located deeper below the nitrided layer. The results have shown that in the hot forging processes carried out in accordance with the adopted technology, the surface layer of working tools is overheated locally to a temperature above 600 °C and tempering occurs. Moreover, overheating effects are visible, because the surface layer is tempered to a depth of 0.3 mm. Finally, such tempering processes lead to a decrease in the die hardness, which causes accelerated wear because of the abrasion and plastic deformation. The nitriding does not protect against the tempering phenomenon, but only delays the material softening process, because tempering occurs in the nitrided layer and in the layers deeper under the nitrided layer. Below the nitrided layer, tempering occurs relatively quickly and a soft layer is formed with a hardness below 400 HV.

МОДЕЛИ МАТЕРИАЛОВ ПРИ ИССЛЕДОВАНИИ ВОЛНОВОГО ДЕФОРМАЦИОННОГО УПРОЧНЕНИЯ МЕТОДОМ КОНЕЧНЫХ ЭЛЕМЕНТОВ

The problem of necessity in the development of loading environment models (materials processed) which has great importance at the finite element simulation of basic processes (technologies) is considered. 
 As a rule, material model programs embedded into CAE cannot be used completely in the computations because of their limited set of physical-mechanical properties, most often insufficient for the adequate simulation of the process under investigation. By the example of the technology of wave deformation strengthening taking into account its peculiarities in the paper for the first time there are developed material models: steel45, BrAZh9-4; VT1-0; B-95 and the estimation of their adequacy is carried out. The creation of each model of material is a unique process and implies not only the pattern completion with data from reference books, but also with data obtained as a result of the fulfillment of corresponding experimental investigations of properties peculiar to material under working. As a result there are developed adequate models of materials having an admissible error (not exceeding 7.4%) for micro-hardness and depth of surface layer strengthening that allows recommending their use at the investigation of wave deformation strengthening through a finite element method.

Formation of Structure and Properties in Titanium under Laser Surface Alloying with Copper

The effect of laser surface alloying with copper on the structure, phase composition and microhardness of surface layers of titanium is studied. Treatment modes improving the structure and special properties of the surface are determined.