Effect of grain size on compressive behaviour of titanium at different strain rates

An investigation was conducted to evaluate the dependence on grain size of the compressive deformation of commercial purity (CP) Ti. Tests were performed at room temperature using grain sizes from coarse-grained CG (20 ?m) to ultrafine-grained UFG (500 nm) and nanocrystalline NC (90 nm) with testing strain rates in the range from 0.01 to 10 s?1. The results show the flow stress and the strain rate sensitivity of CP Ti increase with decreasing grain size. Work hardening dominates at all strain rates in CG Ti but it balances with flow softening at 0.01 and 0.1 s?1 in UFG and NC Ti and there is obvious flow softening in these two materials at 10 s?1

Nanomaterials by severe plastic deformation: review of historical developments and recent advances

International audienceSevere plastic deformation (SPD) is effective in producing bulk ultrafine-grained and nanostructured materials with large densities of lattice defects. This field, also known as NanoSPD, experienced a significant progress within the past two decades. Beside classic SPD methods such as high-pressure torsion, equal-channel angular pressing, accumulative roll-bonding, twist extrusion, and multi-directional forging, various continuous techniques were introduced to produce upscaled samples. Moreover, numerous alloys, glasses, semiconductors, ceramics, polymers, and their composites were processed. The SPD methods were used to synthesize new materials or to stabilize metastable phases with advanced mechanical and functional properties. High strength combined with high ductility, low/room-temperature superplasticity, creep resistance, hydrogen storage, photocatalytic hydrogen production, photocatalytic CO2 conversion, superconductivity, thermoelectric performance, radiation resistance, corrosion resistance, and biocompatibility are some highlighted properties of SPD-processed materials. This article reviews recent advances in the NanoSPD field and provides a brief history regarding its progress from the ancient times to modernity

Room Temperature Superplaticity in Fine/Ultrafine Grained Materials Subjected to Severe Plastic Deformation

Demirtas, Muhammet/0000-0002-7357-3892WOS: 000472621600009Achieving superplasticity at high temperatures and at very low strain rates is considered to be the most important disadvange of superplastic forming processes. Therefore, it is crucial to achieve superplastic behavior at low temperatures and high strain rates. To do so, it is well known that, high amount of grain refinement in the superplastic material is required. Very recent advances in severe plastic deformation (SPD) techniques based on imposing very high strains to the material provide abnormal grain refinement, and ultrafine-grained (UFG) microstructures can be achived in metallic materials by this manner. Formation of UFG microstructures via SPD methods like equal channel angular pressing (ECAP), high pressure torsion (HPT) and friction stir processing (FSP) bring about superplastic behavior in some classes of alloys even at room temperature (RT) as an extreme example of low temperature superplasticity. This paper overviews the studies aiming to investigate the RT superplasticity in some specific metals and alloys after UFG formation by SPD methods. UFG formation or nanostructuring of the materials by SPD to attain RT superplasticity were analyzed in detail. Also, the parameters affecting the RT superplasticity in different classes of materials and superplastic deformation mechanisms operated at RT superplasticity were explained.Scientific Research Projects of Karadeniz Technical University, TurkeyKaradeniz Technical University [no10501]This research was supported by Scientific Research Projects of Karadeniz Technical University, Turkey, under Grant no10501. the authors of this study are also grateful to the authors of the reviewed papers for their great studies

Enhancing the Damping Behavior of Dilute Zn-0.3Al Alloy by Equal Channel Angular Pressing

The effect of grain size on the damping capacity of a dilute Zn-0.3Al alloy was investigated. It was found that there was a critical strain value (?1 × 10 ?4 ) below and above which damping of Zn-0.3Al showed dynamic and static/dynamic hysteresis behavior, respectively. In the dynamic hysteresis region, damping resulted from viscous sliding of phase/grain boundaries, and decreasing grain size increased the damping capacity. While the quenched sample with 100 to 250 µm grain size showed very limited damping capacity with a loss factor tan? of less than 0.007, decreasing grain size down to 2 µm by equal channel angular pressing (ECAP) increased tan? to 0.100 in this region. Dynamic recrystallization due to microplasticity at the sample surface was proposed as the damping mechanism for the first time in the region where the alloy showed the combined aspects of dynamic and static hysteresis damping. In this region, tan? increased with increasing strain amplitude, and ECAPed sample showed a tan? value of 0.256 at a strain amplitude of 2 × 10 ?3 , the highest recorded so far in the damping capacity-related studies on ZA alloys. © 2017, The Minerals, Metals & Materials Society and ASM International

Friction Stir Welding of Low-Carbon Shipbuilding Steel Plates: Microstructure, Mechanical Properties, and Corrosion Behavior

Aktarer, Semih Mahmut/0000-0001-5650-7431WOS: 000477997600019In this study, low-carbon steel plates (ASTM 131A) used generally in shipbuilding applications were joined by friction stir welding (FSW) using optimum processing parameters. the microstructure, mechanical properties, formability, and corrosion behavior of the joint were investigated. From the results of the investigation, it was discovered that two distinct regions, stir zone (SZ) and heat-affected zone (HAZ), were formed in the welded region during FSW of the plates. FSW decreased the ferritic grain size of the SZ from 25 mu m to about 4 mu m. Refined grains were separated mostly by a high angle of misorientation with the low amount of dislocations. the hardness of the SZ increased from 140 Hv0.3 to about 230 Hv0.3. the yield and tensile strength values of the SZ increased from 256 and 435 MPa to about 457 and 585 MPa, respectively, by the effect of FSW without a considerable decrease in ductility. FSW did not cause a significant change in the formability of the joint. Displacement at the maximum bending force decreased slightly after FSW from 6.31 mm to about 5.69 mm. Also, corrosion resistance after FSW slightly increased as a result of grain refinement. Current density values were obtained as 3.36 x 10(-6) A/cm(2) (base material 4.44 x 10(-6) A/cm(2)).The World Academy of Sciences (TWAS) under the Visiting Researchers Program of TWAS-UNESCO Associateship Scheme [3240260896]Dr. G. Purcek was supported by "The World Academy of Sciences (TWAS) under the Visiting Researchers Program of TWAS-UNESCO Associateship Scheme (Ref. 3240260896)." the authors would like to thank Dr. T. Kucukomeroglu for his help in conducting the FSW

An upper-bound analysis for equal-channel angular extrusion

Deformation of the material during a 90° equal-channel angular extrusion (ECAE) process is analyzed using upper-bound theorem. The model suggested includes the effect of friction between the sample and the die walls, radius of inner corner of the die and the dead metal zone on the deformation patterns during ECAE. The parameters of the model is explored in relation to the deformation of the material during the process. Further directions for progress in deformation analysis in severe plastic deformation processes are outlined. © 2004 Elsevier B.V. All rights reserved