Intermediate Heat Treatment Research Articles

Ti/Al Multi-Layered Sheets: Differential Speed Rolling (Part B)

Differential speed rolling has been applied to multi-layered Ti/Al composite sheets, obtained from accumulative roll bonding with intermediate heat treatments being applied. In comparison to conventional rolling, differential speed rolling is more efficient in strengthening the composite due to the more pronounced grain refinement. Severe plastic deformation by means of rolling becomes feasible if the evolution of common rolling textures in the Ti layers is retarded. In this condition, a maximum strength level of the composites is achieved, i.e., an ultimate tensile strength of 464 MPa, while the strain to failure amounts to 6.8%. The deformation has been observed for multi-layered composites. In combination with the analysis of the microstructure, this has been correlated to the mechanical properties.

280 kJ/m<sup>3</sup>高鉄濃度サマリウムコバルト磁石の開発・実用化

We have developed Sm2Co17 sintered magnets whose Fe concentration is much higher than conventional Sm2Co17 sintered magnets. The pre-aging treatment leads to fine cell structure and improvement in squareness of demagnetization curves. As a result the (BH)max of pre-aged magnets shows higher than that of no-pre-aged magnet. The inter-mediate heat treatment (IHT) induces the grain growth. We found that squareness of demagnetization curve has clearly improved by the IHT at adequate temperature. These results indicate that reducing the fraction of grain boundaries by increasing the grain size affects the behavior of domain-wall motion. Sm2Co17 sintered magnets fabricated adopting pre-aging treatment and IHT show (BH)max of 282 kJ/m3.

Solution-processed multilayered BiVO4 photoanodes: influence of intermediate heat treatments on the photoactivity

Intermediate heat treatments to at least 350 °C are needed to obtain fully crystalline monoclinic BiVO4 films with tunable thickness from spin coating of successive layers from a precursor solution.

Study on Orange Peel Phenomena in Cu-Cr-Zr-Ti Alloy Thrust Chamber

Cu-Cr-Zr-Ti alloys are widely used for fabrication of thrust chamber in liquid rocket engines, because of their high thermal conductivity and adequate strength. The alloy should be used in peak aged condition to achieve the best combination of strength and conductivity. However, realization of final component involves different stages of forming, intermediate heat treatment and brazing operations, which limit the usage of the alloy in peak aged condition. The formability of material depends on grain size to a large extent. Larger grained metals have better formability, but the roughened surface that results from stretching metal with coarse grain structure results in surface defects like orange peel. Copper alloys on cold working sometimes exhibit a surface pebbling effect termed as ‘orange peel’ or alligator skin’.The plates of this copper alloy, finish hot rolled at 925 to 975°C and annealed at 980±10°C for 10 ±2 min followed by air cooling are subjected to different stages of forming to get the final profile of thrust chamber. During the course of forming of plate for divergent thrust chamber, orange peel defect is observed in areas of higher deformation. Detailed characterization of these formed shells in terms of microstructure, grain size and mechanical property has been carried out to find out the exact cause of this defect. Study revealed that the plate has coarse grain structure, which has resulted in orange peel defect during forming. To overcome this effect, the plates were realized with modifications in finish hot rolling and annealing temperatures, which has shown improvement in grain refinement and mechanical properties. It has suppressed the orange peel defect during forming.

Comparison of 15Cr-15Ni Austenitic Steel Cladding Tubes Obtained by HPTR Cold Pilgering or by Cold Drawing

Due to their high void swelling resistance, work-hardened titanium stabilized austenitic steels have been chosen as cladding material for sodium cooled fast reactor. In this study, HPTR cold pilgering process is compared to cold drawing at the last shaping step of the tube processing. The effects of the cold work accumulation and heat treatments are studied in connection with the microstructure (grain size), the hardness and the texture. The following results were found:- As larger amount of cold work can be applied by HPTR cold pilgering, a lower number of intermediate heat treatments are required. In addition, the bending of the tube is significantly reduced after each pass for this process allowing for a limitation of the straightening operations.- For both processes, optical micrographs show micrometric titanium carbide precipitates and the presence of deformation twins on a few grains on the final tube. A significant grain size refinement from ≈45 μm to ≈17 μm can be obtained by reducing annealing temperature from 1403K down to 1353K. For the latter, the precipitated mass fraction measured by selective dissolution of the alloy matrix is the largest, revealing a possible negative impact on swelling under irradiation.- Through-wall Vickers hardness profiles show an increase of the hardness at the outer diameter for HPTR cold pilgering whereas the hardness profile remains continuous for cold drawing. It is found that the Q-factor has an influence on these wall-thickness hardness profiles.- For each process, neutron diffraction measurements on finished tubes reveal two main fiber texture components 〈111〉 and 〈100〉 parallel to the tube axis with differences in their relative intensities.

Comparative study of the influence of Ag on the microstructure and mechanical properties of Cu-10Fe in situ composites

Cu-10Fe and Cu-10Fe-3Ag in situ composites were prepared by casting and drawing. The microstructure and properties of the composites were investigated in detail. Results show that the presence of Ag can refine the primary Fe dendrites, which leads to a significantly higher strength of Cu-Fe-Ag composites. For each deformation strain, the tensile strength of the cold-worked Cu-10Fe-3Ag in situ composite was 66 MPa–230 MPa higher than that of the Cu-10Fe in situ composite, and the conductivity of the cold-worked Cu-10Fe-3Ag in situ composite was 1%–4% IACS higher than that of the Cu-10Fe in situ composite. The Cu-10Fe-3Ag in situ composites had a combination of properties with intermediate heat treatment. After 1 h of heat treatment at 450 °C, the tensile strength increased to 968 MPa, and the conductivity increased to 62.6% IACS.

Effect of intermediate annealing on the microstructure and mechanical property of ZK60 magnesium alloy produced by twin roll casting and hot rolling

Twin roll cast (designated as TRC in short) ZK60 magnesium alloy strip with 3.5mm thickness was used in this paper. The TRC ZK60 strip was multi-pass rolled at different temperatures, intermediate annealing heat treatment was performed when the thickness of the strip changed from 3.5mm to 1mm, and then continued to be rolled until the thickness reached to 0.5mm. The effect of intermediate annealing during rolling process on microstructure, texture and room temperature mechanical properties of TRC ZK60 strip was studied by using OM, TEM, XRD and electronic universal testing machine. The introduction of intermediate annealing can contribute to recrystallization in the ZK60 sheet which was greatly deformed, and help to reduce the stress concentration generated in the rolling process. Microstructure uniformity and mechanical properties of the ZK60 alloy sheet were also improved; in particular, the room temperature elongation was greatly improved. When the TRC ZK60 strip was rolled at 300°C and 350°C, the room temperature elongation of the rolled sheet with 0.5mm thickness which was intermediate annealed during the rolling process was increased by 95% and 72% than that of no intermediate annealing, respectively.

Effect of pressing routes on the microstructure and strength in equal channel angular pressing of Cu-3.75Ag

The combined effects of thermo-mechanical treatment and equal channel angular pressing (ECAP) on the strength and microstructure of Cu-3.75Ag were studied. The strength of Cu-3.75Ag at 1% strain after eight passes of ECAP with two intermediate heat treatments reached 758 MPa and 849 MPa in route A and route Bc respectively. The hardness increased upon heat-treatment in route Bc, in contrast to the drop of the hardness in route A, suggesting that the hardening caused by re-precipitation is more active due to more effective dissolution of second-phase particles in route Bc. The flow stress increased more rapidly with intermediate heat treatments and reached 842 MPa after 8 passes, greater than that (791 MPa) without intermeadiate heat treatment in route Bc. The more rapid increase of strength/hardness and the attainment of higher hardness/strength after intermediate heat treatment are likely to be attributed to the formation of more stable wall structure and rearrangement of solute atoms/precipitates. The spacing between precipitates in Cu-3.75Ag ECAPed for 4 pass in route Bc was measured to be approximately 12.5 nm, which is close to the calculated activated length (12.8 nm). The most probable rate controlling mechanism of Cu-3.75 Ag is suggested to be the interaction between dislocations and precipitates.

The Study of Nb<sub>3</sub>Sn Phase Formation Process in Multifilamentary Superconductors for High-Magnetic-Field Systems

Recent investigations of the connection between the microstructure and the properties of Nb 3 Sn superconductors produced by the bronze method, for the large ITER magnets, have enabled us to develop wire fabrication technologies and to manufacture large quantities of such material that met all the technical requirements. The next stage is to study the possibility of increasing the critical current properties in a wide range of magnetic fields with the aim to apply them in the next generation of magnetic systems. In this study, the superconducting phase formation process, its structure, and the composition and critical properties of various layouts of Nb 3 Sn wire used under magnetic fields of 12-16 T have been investigated. It is shown that the intermetallic compound structure heavily depends on the grain structure of niobium filaments produced by multiple deformation of the composite wire with intermediate heat treatments. It is concluded that the improvement of the superconducting phase structure and the increase in current-carrying capability of wire in high magnetic fields are possible by the fine grain structure of initial niobium filament and an increase in the tin content of the bronze matrix.

Influence of Intermediate Annealing on the Nanostructure and Mechanical Properties of Pure Copper Processed by Equal Channel Angular Pressing and Cold Rolling

The effects of intermediate heat treatment on the nanostructure and the mechanical properties of pure copper samples processed by four passes of equal channel angular pressing (ECAP) and cold rolling (CR) with a total reduction of 55 pct were investigated. The annealing treatments were done at 423 K, 463 K, and 523 K (150 °C, 190 °C and 250 °C) for 15 minutes. Microstructural examinations revealed no trace of a recrystallization after annealing at 423 K (150 °C). X-ray diffraction analysis illustrated that employing annealing treatment at 463 K (190 °C) decreased the coherent domain size and, consequently, increased the microstrain value. Moreover, nucleation of the newly formed grains resulted from discontinuous static recrystallization decreased the mean grain size. The yield and the tensile strength were also enhanced due to the reduction of the coherent domain size, the internal stress augmentation, and the presence of the new fine grains. Annealing at 523 K (250 °C) increased the fraction of the recrystallized structure and, consequently, decreased the fraction of the grains created by ECAP. As a result, the typical rolling texture intensified.

Research in the Field of Manufacturing of Layered Brazing Materials

The results of research into manufacturing of layered brazing materials with silver brazing alloy BAg22 content and copper obtained in pressing at elevated temperature and rolling process for use in cutting tools working in harsh conditions were presented. Mechanical and dimensional properties of the constituent materials of the layered strips with 50 and 75% volume fraction of copper as the inner layer were selected, i.e. the BAg22 alloy strip and the copper strip, for the preliminary join operation in pressing process. Cladding process conditions of the set BAg22/Cu/BAg22 of the original thickness of 32mm for the ratio of layer thicknesses as 1:2:1 and 24mm of the original thickness for the ratio of layer thicknesses as 1:6:1 including the method of semi products surface preparation and range of forces and temperature parameters were specified. Plastic working conditions of pressed composite ingot in hot and cold rolling to the final thickness with the intermediate and final heat treatment parameters were developed.

DRAWING OF SOLID REGULAR POLYGONAL SECTION SHAPES

In designing the regular polygonal section shape drawing process, it is convenient to use analytical expressions allowing us to estimate effectively the effect of different process factors. A design procedure of stress calculation for this process is proposed. The ratios for calculation of drawing stress, optimum angle of the drawing tool hole, limit value of deformation degree in using the standard tool and index of stress state in the axial part of the deformation zone are obtained. The use of drawing tools with optimum angles reduces the accumulation rate in the metal structure and in case of repeated drawing allows us to cut down the number of intermediate heat treatments.

Effect of Intermediate Heat Treatment on the Mechanical Properties of 3003/4343 Aluminum Clad Sheet Manufactured by Strip Casting/Clad Rolling

Effect of intermediate heat treatment on the microstructure evolution and mechanical properties of A3003/A4343 clad sheet manufactured through new processes were investigated. Raw materials® both A3003 and A4343 alloys®were fabricated by twin roll strip casting process, and then cold rolling and roll bonding were performed with final thickness of 215μm. In the manufactured clad sheets, the thickness of 3003 alloy was found to be 191μm, and that of 4343 alloy, 24 μm. Rolled and recovered microstructures appeared at low heat treatment temperatures (260°C, 280°C), and recrystallization/grain growth were noted from the A3003/A4343 interfaces at 573K or higher temperatures, with the area (recrystallization/grain growth) gradually increasing as heat treatment temperatures increased further. According to the results of tensile tests, yield strength was 223.7MPa, and tensile strength was 270MPa in as-rolled state. As the intermediate heat treatment temperature increased, strengths continuously decreased, whereas elongation exhibited an increasing tendency. Until the final tensile fracture, 3003 alloy and 4343 alloy were not separated but maintained well in bonded state. Based on the results of microstructure evolution by which microstructures were divided into three areas and changed following intermediate heat treatment, the tensile properties of A3003/A4343 clad sheets were analyzed and discussed. [doi:10.2320/matertrans.M2014298]

Innovative Aluminium Lightweight Design by the Combination of Accumulative Roll Bonding and Local Intermediate Heat Treatment

The intensifying regulations for CO2 emissions of passenger cars lead to increased efforts in the field of lightweight construction. In this context, the application of aluminium is a promising strategy. Another approach is the implementation of high strength materials to enable the reduction of the wall thickness of components and to ensure the crash performance. The manufacturing of multi-layered aluminium sheet metal with enhanced strength and nanocrystalline grain structure can be performed using the Accumulative Roll Bonding process (ARB). However, the formability of ARB processed aluminium is relatively poor. Therefore, within this paper an innovative approach to enhance the formability is presented. Key idea of the local short term intermediate heat treatment is the tailoring of the mechanical properties between two forming operations. In order to identify suitable process parameters for beneficial heat treatment, the interaction of pre-straining and heat treatment is evaluated.

Effect of Iron Content on the Strength and Conductivity of Cu-Fe <i>In Situ</i> Composite

Cu-14Fe and Cu-17Fe alloys were produced by casting and processed into in situ composites by hot and cold deformation, and intermediate heat treatment. The microstructures were investigated by using a scanning electron microscope and an optical microscope. The electrical conductivity was evaluated by using a digital micro-ohmmeter. The tensile strength was measured by using an electronic tensile-testing machine. The results show that there are similar cast and deformation microstructures in Cu-14Fe and Cu-17Fe. The tensile strength of deformation-processed Cu-17Fe in situ composite is much higher than that of Cu-14Fe, while the conductivity of deformation-processed Cu-17Fe in situ composite is slightly lower than that of Cu-14Fe at the same cold deformation strain. The Cu-17Fe in situ composite produced by using proper thermo-mechanical processing possesses a good combination of tensile strength and electrical conductivity.

Drawing Tantalum Encapsulated in the Cooper Pipe

Tantalum has characteristics such as excellent ductility, high corrosion resistance, high mechanical strength at high temperatures and high resistance to etching of acids and bases. Its high ductility allows the realization of large reductions without the need for intermediate heat treatment. A process for the production of tantalum wire is drawing. However, when using this process, the high ductility of the tantalum (Ta) metal causes a retention/accumulation of the Ta in the spinneret. Therefore, to be drawn is necessary that the tantalum is encapsulated in a copper tube. In this work was produced a Ta wire by means of rotary forging and drawing process. In the drawing process of the tantalum encapsulated in copper tube, was the appearance of striation on the surface of tantalum, when applied to an area reduction (AR) of approximately 22%. This fact is possibly related to the different sliding systems with consequent formation of non-hydrostatic stress fields at the interface Cu / Ta. After an area reduction (AR) of 94% the Cu was removed from the surface of the wire, through chemical etching, and this wire was drawn up to 0.43mm without retention/accumulation of the Ta in the spinneret.

Study on the effect of heat treatment conditions on metalorganic-chemical-vapor-deposited ferroelectric Hf0.5Zr0.5O2 thin film on Ir electrode

The effect of the heat treatment conditions on the constituent phases and electrical properties of (Hf0.5Zr0.5)O2 films deposited by the metalorganic chemical vapor deposition was investigated. By using a low temperature or short duration for post-heat treatment after the deposition, the volume fraction of the tetragonal phase increases, resulting in a high dielectric constant. On the other hand, the volume fraction of the monoclinic phase increased in the films that were heat-treated at higher temperatures and exposed to longer heat treatment duration. The ferroelectric with and dielectric properties of these films were greatly inferior. Superior ferroelectric properties a significant volume fraction of orthorhombic phase were achieved for intermediate heat treatment conditions. These results give useful information to understand the origin of the ferroelectricity and to control the phases and electrical properties in HfO2-based films.

Improving high temperature creep resistance of reduced activation steels by addition of nitrogen and intermediate heat treatment

In the present study, we report an enhanced high-temperature creep resistance in reduced activation ferrite/martensite (RAFM) steels, by introducing nitrogen (0.035wt%, M3 steel) and employing a novel intermediate heat treatment I–Q–T (intermediate treatment, quenching and tempering). In comparison with all the control groups, the uniaxial tests of the I–Q–T treated M3 steel showed significant increase in rupture time and decrease in elongation. The microstructures of the samples were further characterized to elucidate the origin of the enhanced creep resistance. It is found that, by introducing nitrogen, the primary TaC particles were refined; by employing the I–Q–T heat treatment, the dispersed fine secondary MX precipitates, as well as the lath subgrains containing high-density dislocations, were increased: all are responsible for the improved creep resistance.

Thermo-mechanical processing, microstructure and tensile properties of a tungsten heavy alloy

The effect of heat treatment and swaging on microstructure and mechanical properties of a tungsten heavy alloy (WHA) of composition 90.5W–7.1Ni–1.65Fe–0.5Co–0.25Mo (wt%) has been examined in this study. The volume fraction and the contiguity of W-grains in the sintered microstructure decrease from 80% to 75% and 0.7 to 0.3, respectively, following an intermediate heat treatment comprising annealing at 1373K followed by oil quenching. The average aspect ratio of W-grain increases with the increase in swaging deformation. While the bulk hardness of the alloy increases with increase in swaging deformation, a minor drop in hardness is observed following intermediate heat treatment. Peak broadening is observed in the X-ray diffractograms following thermo-mechanical processing with full width at half maxima (FWHM) of W110 peak exhibiting a similar trend as that of hardness. The as-sintered alloy exhibits low yield strength, tensile strength and very low elongation to failure. Subsequent thermo-mechanical treatment results in substantial improvement of both strength and elongation. A strength value of 1427MPa with elongation of 5–6% has been achieved following 40% swaging. Work hardening behavior of the alloy in heat treated condition has been studied and the results are correlated with slip lines and dislocation behavior of the alloy.

Forming limits of an age hardenable aluminum sheet after pre-straining and annealing

Abstract A two-stage stamping with an intermediate annealing method was developed to improve formability of age hardenable aluminum alloys, which are more challenging than the non-age hardenable aluminum alloys because of the effects that intermediate annealing will have on dissolution of solutes, precipitation of strengthening particles, and the subsequent mechanical behavior of the materials. The process could readily be applied locally to highly strained areas of a complex panel for 6000 series aluminum alloys in order to form a good part without fracture; however, there will be a decrease of precipitation strengthening of those locally treated, highly strained areas. In this study, the strain-based forming limit curves (FLC) of as-received AAx610-T4PD alloy sheets were shown to increase after pre-straining to ~15% and annealing at 425 °C for 10 s. However, since strain-based FLCs are very sensitive to the pre-strain history, both stress-based FLCs and polar-effective-plastic-strain (PEPS) FLCs, which are path-independent, were used to evaluate the forming limits after pre-straining and annealing. Due to the change of mechanical behavior during annealing, this paper describes the procedure to calculate the stress-based FLC in which a residual-effective-plastic-strain (REPS) is determined by overlapping the hardening curve of the pre-strained and annealed material with that of material heat treated without pre-strain. After converting the strain-based FLCs using the constant REPS method, it was found that the stress-based FLCs and the PEPS FLCs of the post-annealed materials are quite similar and both tools are applicable for evaluating the forming limits of Al–Mg–Si alloys for the two-step stamping process with intermediate annealing heat treatment.