Combined Thermomechanical Treatment Research Articles

Effect of combined thermomechanical treatment on structure, mechanical properties, electrochemical behavior and functional corrosion fatigue of biodegradable Fe-30Mn-5Si alloy

In present study, the combined thermomechanical treatment (TMT), including the radial-shear rolling (RSR) at 900 °C followed by longitudinal rolling (RSR+LR) at 700 °C, was applied to biodegradable Fe-30Mn-5Si (wt%) alloy. The effect of these TMTs on the microstructure, phase composition, mechanical properties (ultimate tensile strength UTS, apparent yield stress σ0.2, relative elongation to failure δ, Young's modulus E), electrochemical behavior and functional corrosion-fatigue behavior in Hanks’ solution were studied. It was found that RSR leads to the formation of a statically recrystallized γ-austenite structure with an average grain size of 10±3 and 20±3 µm in the peripheral and central zones, respectively. The RSR+LR results in a mixture of dynamically recrystallized and dynamically polygonized structures with the average grain size of 5±1 µm. Moreover, RSR and RSR+LR lead to the formation of a single-phase FCC γ-austenite state compared to reference heat treatment (RHT), where microstructure is characterized by a two-phase state of FCC γ-austenite and HCP ε-martensite with an average grain size of 200–300 µm. Based on static mechanical tensile tests to failure, it was established that RSR and RSR+LR lead to a significant increase of UTS up to 770±21 and 935±55 MPa, σ0.2 up to 300±38 and 490±43 MPa, and δ up to 28±2 and 19±10 %, while maintaining acceptable of E value about 165±29 and 150±8 GPa, respectively as compared to 460±41 MPa, 210±91 MPa, 11±3 %, and 140±14 GPa after RHT. The electrochemical studies showed that single-phase structure (FCC γ-austenite) formed after RSR and RSR+LR leads to the non-critical biodegradation rate lowering as compared to the two-phase state (γ-austenite and ε-martensite) after RHT. Besides RSR and RSR+LR lead to significant improvement of functional corrosion-fatigue life in Hanks’ solution.

Synergistic effects of trace silicon, calcium and cerium on the microstructure and properties of a novel Cu–Cr–Nb–Si–Ca–Ce alloy

In this paper, a novel Cu-0.60Cr-0.20Nb-0.05Si-0.02Ca-0.02Ce (CCNSCC, wt.%) alloy is designed. By comparing the differences in the properties and microstructure with the Cu-0.60Cr-0.20Nb (CCN, wt.%) alloy under the same process, the effects of trace Si, Ca, and Ce elements on the CCNSCC alloy are disclosed. After undergoing cold rolling by 80% and aging at 450 °C for 60 min, the CCNSCC alloy exhibits a tensile strength of 524 MPa and a softening temperature of 600 °C. These values represent an increase of 104 MPa and 90 °C respectively compared with the CCN alloy. After a multi-stage combined thermo-mechanical treatment including preaging at 400 °C for 30 min, the tensile strength and electrical conductivity of the CCNSCC alloy reach 618 MPa and 75.2%IACS respectively. Microstructure analysis shows the existence of rod-like and polygonal Cr8Nb3Si particles, as well as globular, ellipsoidal, and crescent-shaped (Ca,Ce)Cu5 particles. During the process of aging, the precipitation of the Cr phase occurs at the phase boundaries of Cr8Nb3Si particles. Additionally, significant quantities of fine Cr particles at the nanoscale surround the Cr8Nb3Si particles, exerting a beneficial influence on the strength and electrical conductivity of the CCNSCC alloy. Besides, the CCNSCC alloy has finer Cr particle size and lower volume fraction of recrystallized grains after aging in comparison to the CCN alloy. This indicates that the addition of trace Si, Ca, and Ce elements significantly inhibits the growth of Cr particles and occurrence of recrystallization. Plenty of dislocations are observed in different states of the CCNSCC alloy, and their interaction with the Cr precipitates is the primary factor contributing to the excellent mechanical properties of the CCNSCC alloy. The findings of this study provide valuable insights for improving the properties and microstructure of Cu–Cr–Nb alloys.

Microstructure and properties of high strength and high conductivity Cu-0.48Cr-0.20Nb-0.27Zn alloy treated by a new combined thermo-mechanical treatment

A Cu-0.48Cr-0.20Nb-0.27Zn (wt.%) alloy with excellent comprehensive performance is designed and prepared by adding Zn element and combining it with a novel combined thermo-mechanical treatment. A high-temperature short-time treatment is introduced to the traditional thermo-mechanical treatment. Results show that the hardness, tensile strength, yield strength, elongation, and electrical conductivity of Cu-Cr-Nb-Zn alloy reach 180HV, 580 MPa, 535 MPa, 7.6%, and 80.2%IACS, respectively. Compared with conventional thermo-mechanical treatment, the alloy after the new process has increased by 15HV, 35 MPa, 40 MPa, 1.3%, and 2.0%IACS, respectively. Submicron grains and nanoscale twins emerge following high-temperature short-time treatment (850 °C/5min), and the grains undergo substantial refinement. Besides, this process promotes the precipitation of solid solution Cr atoms, thereby significantly improving the electrical conductivity of the alloy. Two distinct crystal structures (C14 and C15) of Cr2Nb with diameters ranging from 80 to 200 nm are observed. The alloy's strength is greatly increased in the following aging process, which precipitates a significant quantity of nanoscale Cr phase. All of the above results have certain reference significance for the optimization design of Cu-Cr-Nb alloy composition as well as performance improvement.

Effect of Cooling and Annealing Conditions on the Microstructure, Mechanical and Superelastic Behavior of a Rotary Forged Ti-18Zr-15Nb (at. %) Bar Stock for Spinal Implants.

In this work, the microstructure, phase state, texture, superelastic and mechanical properties of a Ti-18Zr-15Nb (at. %) shape memory alloy subjected to a combined thermomechanical treatment, including hot rotary forging with either air cooling or water quenching and post-deformation annealing are studied. It was revealed that the main structural component of the deformed and annealed alloy is BCC β-phase. With an increase in the forging temperature from 600 to 700 °C, the average grain size increases from 5.4 to 17.8 µm for the air-cooled specimens and from 3.4 to 14.7 µm for the water-quenched specimens. Annealing at 525 °C after forging at 700 °C with water quenching leads to the formation of a mixed statically and dynamically polygonized substructure of β-phase. In this state, the alloy demonstrates the best combination of functional properties in this study: a Young's modulus of ~33 GPa, an ultimate tensile strength of ~600 MPa and a superelastic recovery strain of ~3.4%.

Tension-compression asymmetry of quadruple CuCoNiBe alloys processed by high-temperature multi-pass equal channel angular pressing (ECAP)

Abstract Among copper alloys, the precipitation (age) hardening quadruple CuCoNiBe alloys due to their superior mechanical properties in terms of the highest strength and elasticity achieved by peak aging have been used over the years in a wide range of industrial applications including aircrafts, coil systems, blast-proof materials, and molding dies. Combined thermomechanical treatment (i.e., equal channel angular pressing [ECAP] processing followed by post-ECAP aging) can result in a further enhancement of the strength of CuCoNiBe alloys due to the grain refinement and the formation of fine precipitates from α-Cu supersaturated solid solution. In this study, for the first time, the effect of severe plastic deformation by ECAP processing on the mechanical behavior of CuCoNiBe alloys is discussed thoroughly based on the material responses to tensile and compressive loading conditions. The results show that, besides a considerable strength enhancement, ECAP processing leads to a strong tension-compression asymmetry and significantly accelerated precipitation kinetics in CuCoNiBe alloys.

Effect of aging treatment and equal channel angular pressing on microstructure evolution and properties of a CuCrZrSc alloy

Precipitation and severe plastic deformation have been proven to be effective methods for separately enhancing the properties of copper alloys. This work studied microstructure evolution and properties of a CuCrZrSc alloy undergoing aging treatment and equal channel angular pressed (ECAP). After 12 passes of combined thermomechanical treatment, the high-angle grain boundary spacing of the alloy was reduced to 300 nm, and many low-angle grain boundaries appeared. When the ECAP deformation reached 8 passes, stacking faults occurred in the grains due to severe shear deformation. After 12 passes, lamellar twins were detected in the sample. The pre-aging treatment before ECAP can refine the microstructure of CuCrZrSc alloy and significantly improve the mechanical properties and electrical conductivities of the alloy. After 12 passes of deformation and aged at 400 °C for 15 min, the studied CuCrZrSc alloy had a UTS of 664 MPa, elongation of 17.5%, and electrical conductivity of 80.1% IACS. Electron back-scattered diffraction and transmission Kikuchi diffraction techniques were employed to analyze the microstructure evolution of samples with different ECAP passes.

Effect of severe plastic deformation on the precipitation kinetics and the properties of CuCoNiBe alloys

The effect of the precipitation hardening by means of the conventional heat treatment and the combined thermomechanical treatment (i.e., equal channel angular pressing (ECAP) with subsequent aging) on the electrical conductivity, mechanical properties and precipitation kinetics of precipitation hardening, quadruple CuCo1Ni1Be alloy was investigated. No experimental studies on the effect of ECAP on the electrical conductivity and precipitation kinetics of CuCoNiBe alloys have been reported. Systematic microstructural and mechanical investigations show that both ECAP processing and post-ECAP aging result in a significant increase in the hardness and strength of the alloy due to the grain boundary strengthening by means of the grain refinement (and the formation of subgrains) and due to the precipitation hardening by means of the formed precipitates (primary and secondary beryllides) in the fine-grained structure, respectively. Moreover, the electrical conductivity of both solution treated and ECAPed alloys increases with increasing aging time due to the precipitation of the solute atoms in α-Cu matrix leading to decreasing electrical resistivity. However, the CuCo1Ni1Be alloys subjected to ECAP exhibit a lower conductivity than the solution treated ones, which can be attributed to an increase in resistivity caused by increased probability of electrons scattering by severe plastic deformation. The linear relationship between electrical conductivity and volume fraction of the precipitates according to the Martition's law and the empirical Avrami equation are used to investigate the precipitation kinetics of the CuCo1Ni1Be alloy. The S-shaped volume fraction of precipitates vs. aging time curves clearly indicate that the precipitation kinetics of the CuCoNiBe alloys can be significantly promoted by ECAP processing. The results of the present study provide new insights into the interaction of the severe plastic deformation, the kinetics of precipitation, and the microstructural, mechanical and physical properties of the CuCo1Ni1Be alloy.

Increasing wear and corrosion resistance of steel products by combined laser thermomechanical treatment

A technique is presented for hardening metal products, in particular, the main tools (hammers) and cases of core drilling bits made of steel 30HGSA, using thermomechanical surface treatment according to a separate scheme. The method of combined laser thermomechanical hardening used in the study consists in the use of shot peening followed by laser heat treatment. Its use makes it possible to increase the operational properties of steel products, in particular, their wear and corrosion resistance. Based on the results of theoretical and experimental studies, the paper substantiates the features of dynamic surface plastic deformation for the analysis of impact during shot peening. The advantages of using laser hardening without surface melting are presented. Experimental research methods are proposed for determining the structural-phase composition, structure of the surface layer, hardness and microhardness of the hardened zones of steel 30HGSA. The range of rational modes of impact shot peening and thermal laser treatment has been determined. A device for testing samples for wear resistance has been developed. Methods of testing for wear and corrosion resistance of the surface of samples are proposed for assessing the tribological properties and contact interaction of materials under quasi-static and dynamic loading conditions. It is concluded that rational technological modes of hardening tools made of steel 30HGSA using combined laser thermomechanical treatment allow increasing the depth of the hardened layer by ~1.5 times compared to laser heat treatment. In addition, they provide the microhardness of the surface layer of ~5400 MPa, which is ~2.5 times higher than the microhardness of the base material

Effect of Severe Plastic Deformation on the Mechanical and Electrical Properties of Cr-modified Cu-Ni-Si Alloys

Copper alloys are widely used in automotive, electronics, petrochemical and nuclear applications due to their good mechanical/ corrosion resistance and conductivity. Although mostly beryllium containing copper alloys are utilized in these industries due to their superior properties. However, due to the toxic effects of beryllium, there is a need for alternative copper alloys. Among the alternative alloys, Cu-Ni-Si alloys known as Corson alloys are commonly preferred. Both alloying and thermomechanical treatments play important roles to attain similar or better properties in this alloy system, compared to the beryllium containing Cu alloys. In this research, a combined thermomechanical treatment is performed in order to characterize the effect of severe plastic deformation and subsequent heat treatments (i.e., precipitation hardening) on strength, hardness and electrical conductivity of Corson alloys modified by Chromium. The copper alloys having different chemical compositions (Cr contents) are processed using equal-channel angular pressing (ECAP) after solution annealing and quenching. The behavior of Cr-modified alloys is characterized in detail and the effect of the combined thermomechanical treatment and of the Cr content on the final mechanical and physical behavior is discussed. The results show that during aging of solution treated alloys containing 0.4, 0.6 and 0.8 wt-% Cr, a significant increase in both hardness and electrical conductivity is observed, and that increasing Cr content also leads to an increase of both properties. After processing by two-pass ECAP, the hardness of all investigated alloys is significantly increased compared with the solution treated state, whereas the electrical conductivity is adversely affected by severe plastic deformation. The mechanical behavior of the ECAPed alloys can be enhanced even further by performing post-ECAP aging. Therefore, it allows us to develop Cu-Ni-Si alloys by severe plastic deformation process, as an alternative to commonly used beryllium containing copper alloys. The preliminary results provide new insights for the development of construction materials that can be used in the electronic industry, high-speed rail systems, aerospace applications and nuclear power plants, which are recently high priority topics.

Fatigue life estimation of welded structures enhanced by combined thermo-mechanical treatment methods

Different post-weld treatment methods are used to strengthen welded joints that are subjected to cyclic loading. Combining High-Frequency Mechanical Impact (HFMI) treatment with Tungsten Inert Gas (TIG) remelting is rather a new concept. In this paper, the fatigue lives of welded transverse attachments treated by HFMI-treatment, TIG-remelting, or the combination of both are estimated using fatigue damage modelling and finite element deletion. The change in local topography and residual stresses due to treatment are evaluated numerically and incorporated in the analysis. The local hardness is measured by a Vickers tester and incorporated by increasing the elemental ultimate strength. The analysis demonstrates the superiority of the combined treatment because of the introduced compressive residual stress and the improvement in topography. The analysis also shows that the damage is less distributed after the combined treatment than both individual treatments. Besides, the capability of the TIG-HFMI combination in treating existing welded structures with remaining embedded fatigue crack is proven. Besides, available fatigue test results on combined TIG-HFMI treatment shows that this combination gives always longer fatigue life than the characteristic fatigue lives of the treated details by any of the treatment methods. However, many aspects such as TIG arc and HFMI indenter positioning, and indentation and fusion depth should be taken into consideration when the combined treatment is to be applied to existing structures.

New Opportunities to Determine the Rate of Wear of Materials at Friction by the Indentation Data

The article is concerned with the determination of physical plasticity δH (the ratio of the plastic strain to the total strain) and yield stress σS by indentation and the application of these characteristics for analysis of the wear rate W during the friction. The experimental part of the work is performed on the AISI O2 and AISI D2 steels, the surface layers of which were hardened by combined thermomechanical treatment consisted of sequential use of laser heat treatment and ultrasonic impact treatment. For the metals, W is shown to be proportional to δH and inversely proportional to σS. The general scheme for the dependence of W on δH is proposed and based on experimental results for tool steels and hard alloys. For the steels, whose wear is caused by the plastic deformation, W increases with increasing δH, and it decreases conversely for hard alloys worn predominantly by the fracture mechanism. The use of physical plasticity δH and yield stress σS, which are calculated using the hardness and Young’s modulus, characterizes both the hardening extent and the wear rate of the surface layers in more full measure and more accurately than the hardness magnitude itself.

Influence of oxygen concentration on the formation features and thermal stability of the V–Cr–W–Zr alloy microstructure under combined treatment conditions

The results of the study of the influence of oxygen concentration on the features of formation and thermal stability of the microstructure of a low-activation vanadium alloy V–Cr–W–Zr after combined thermomechanical plus chemical-heat (internal oxidation) treatment are presented. Using scanning and transmission electron microscopy, the structural-phase state of this alloy was studied depending on the duration of internal oxidation. The regularities of propagation of the front of internal oxidation with the formation of fine ZrO2 particles are revealed. It was established that the formation of these particles is carried out by the mechanism of nonequilibrium internal oxidation. The implementation of this mechanism ensures uniform conditions for the nucleation and growth of zirconium oxides and a high dispersion of the heterophase structure. It is shown that the features of oxygen distribution at different distances from the surface determine the thermal stability of the microstructure and the level of microhardness. The analysis of thermal stability of fine-disperse heterophase structure of the V–Cr–W–ZrO2 alloy depending on chemical-heat treatment regimes was carried out.

Effect of a combined thermomechanical treatment on the microstructure, texture and superelastic properties of Ti-18Zr-14Nb alloy for orthopedic implants

In this study, different thermomechanical treatment (TMT) routes, combining hot, warm and cold rotary forging with post-deformation annealing at different temperatures, were applied to Ti-18Zr-14Nb shape memory alloy to study the influence of these TMTs on the phase composition, structure, texture, mechanical properties, and superelastic behavior of long-length rod stock for fabrication of load-bearing orthopedic implants. The warm and hot forging routes led to the formation of a dynamically recrystallized structure, most likely combined with a dynamically polygonized structure, with an average β-phase grain size of 9 μm (warm forging) and 30 μm (hot forging). After the combination of warm/hot and cold forging with annealing at 525 °С, the alloy exhibited a polygonized β-phase substructure and the best combination of functional properties: low Young’s modulus (37 GPa), large difference between the dislocation and transformation yield stresses (320 GPa), and significant total amount of superelastic and elastic recovery strains (∼4%).

The effect of combined thermomechanical treatment on the structure, phases and hardness of a superelastic Ti-Zr-Nb bar stock

The superelastic Ti-19Zr-14Nb (at.%) alloy was subjected to a novel sequence of thermomechanical treatment, including radial shear rolling, rotary forging and post-deformation annealing. The features of the grain structure, phase composition and hardness of a long-length bar stock for fabrication of bone implants were analyzed. It was shown that after the aforementioned combined thermomechanical treatment followed by annealing in the 550-750 °C temperature range, the produced bar stock demonstrates uniformly distributed grains of β-phase and uniform hardness across its section.

Effect of Ni/Si Mass Ratio and Thermomechanical Treatment on the Microstructure and Properties of Cu-Ni-Si Alloys.

The effect of the Ni/Si mass ratio and combined thermomechanical treatment on the microstructure and properties of ternary Cu-Ni-Si alloys is discussed systematically. The Cu-Ni-Si alloy with a Ni/Si mass ratio of 4–5 showed good comprehensive properties. Precipitates with disc-like shapes were confirmed as the Ni2Si phase with orthorhombic structure through transmission electron microscopy, high-resolution transmission electron microscopy, and 3D atom probe characterization. After the appropriate thermomechanical treatment, the studied alloy with a Ni/Si mass ratio of 4.2 exhibited excellent mechanical properties: a hardness of 290 HV, tensile strength of 855 MPa, yield strength of 782 MPa, and elongation of 4.5%. Compared with other approaches, the thermomechanical treatment increased the hardness and strength without sacrificing electrical conductivity. Theoretical calculations indicated that the high strength was primarily attributed to the Orowan precipitation strengthening and secondarily ascribed to the work hardening, which were highly consistent with the experimental results. The appropriate Ni/Si mass ratio with a low content of Ni and Si atoms shows high strength and excellent electrical conductivity through combined thermomechanical treatment. This work provides a guideline for the design and preparation of multicomponent Cu-Ni-Si-X alloys with ultrahigh strength and excellent electrical conductivity.

Thermomechanical Treatment of Metal Composite Fractions

AbstractThe investigation focuses on shredder light fractions, electrical waste, and metal concentrates from landfills that can be treated mechanically only with difficulty. The fractions were input to a combined thermomechanical treatment to procure a high degree of composite component separation. Suitable process parameters were identified and the respective treatment outcomes evaluated. Overall, it was possible to verify the basic suitability of the thermomechanical treatment of metal‐rich composite mixtures for recovering the metals contained.

Change in Copper Microstructure and Mechanical Properties with Deformation in an Equal Channel Stepped Die

The effect of prior heat treatment and equal channel angular extrusion (ECAE) in a stepped die on the microstructure and properties of copper M1 is studied. Grain size, microhardness, strength and ductility properties are determined for copper after ECAE. Combined thermomechanical treatment is proposed facilitating an improvement in a set of copper properties.

Combined Thermomechanical Treatment for the Mining Industry

A new method for combined thermo-mechanical treatment of steel 0.4 % C, 1.5 % Cr, 1.5 % Ni, 0.5 % Mo is developed. Thermo-mechanical processing includes hot forging and rapid cooling to the temperature range between the beginning and end of martensitic transformation. The final stage of heat treatment is heating up to the temperature of bainite transformation in which the remaining austenite transforms into a bainite structure and previously formed martensite tempers. In comparison with well known techniques of thermal treatment, the developed thermo-mechanical treatment increases the impact toughness of the steel by 2 times and fatigue crack resistance by 6 times (with equal values of strength parameters). The technological process of high-temperature thermo-mechanical treatment is recommended for treatment of high-strength blank forging.

Strong and Ductile Martensitic Steels for Automotive Applications

The limits of strength and ductility of a medium‐carbon silicon chromium spring steel are investigated for the case of conventional heat treatment including austenitization, quenching and tempering. The effect of phosphorus and austenite deformation prior to quenching was studied by measuring mechanical properties after quenching and tempering and by microstructural investigation. Strong influence of phosphorus on the ductility is observed for the quenched and tempered martensite without prior austenite deformation. The minimum in ductility found after tempering at 350°C is explained by the formation of cementite and grain boundary segregation of phosphorus. Two thermomechanical treatments were tested involving different austenite conditions produced by variation of the deformation temperature. The deformed conditions, recrystallized or work‐hardened, exhibit higher ductility at all tempering temperatures tested. A combined thermomechanical treatment is proposed that provides the highest ductility after tempering at 300°C independent of the phosphorus content. All thermomechanical treatments described in this study refine or eliminate carbide films at prior austenite grain boundaries. It was found possible to increase the tensile strength and the fatigue limit by deformation of austenite prior to quenching while maintaining or increasing the ductility level.

Influence of combined thermomechanical treatment on impurity segregation in ferritic–martensitic and austenitic stainless steels

In this study 13Cr2MoVNb ferritic–martensitic steel (FMS) and 16Cr15Ni3MoNb austenitic stainless steel (ASS) tensile specimens were subjected to standard heat treatments and divided into two groups. Specimens in group 1 (FMS only) were aged at 400°C in a stress free and in an elastically stressed state with a tensile load (100 MPa) then doped with hydrogen in an electrolytic cell. Specimens in group 2 were subjected to cold work (up to 10%) and exposed to short-time heating at 500° for 0.5 h. All specimens were fractured at room temperature in an Auger spectrometer and Auger analysis of the fracture surfaces was performed in situ after fracturing. A noticeable increase of N and P segregation levels and a widening of the depth distribution on the grain boundary facets were observed in the FMS after aging in the stressed state. Cold-worked FMS and ASS showed a ductile dimple mode of fracture, but relatively high levels of S, P and N were observed on the dimple surfaces. We consider the origin of such effects in terms of the stressed state and plastic-deformation-enhanced segregation.