Topic
Ductility
About: Ductility is a research topic. Over the lifetime, 23427 publications have been published within this topic receiving 420674 citations.
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TL;DR: In this paper, the authors presented the various types of microstructure of the Ti-6Al-4V alloy after post-fabrication heat treatments below or above the β transus.
Abstract: Selective laser melting (SLM) is a rapid manufacturing process that enables the buildup of very complex parts in short delays directly from powder beds. Due to the high laser beam energy during very short interaction times and the high solidification rates of the melting pool, the resulting microstructure is out-of-equilibrium and particularly textured. This type of as-fabricated microstructure may not satisfy the aeronautical criterion and requires post heat treatments. Optimized heat treatments are developed, in one side, to homogenize and form the stable phases α and β while preventing exaggerated grain growth. In the other side, heat treatment is investigated to relieve the thermal stresses appearing during cooling. This study is aimed at presenting the various types of microstructure of the Ti-6Al-4V alloy after postfabrication heat treatments below or above the β transus. Tensile tests are then carried out at room temperature in order to assess the effect of the microstructures on the mechanical properties. The fine as-fabricated microstructure presents high yield and ultimate strengths, whereas the ductility is well below the standard. A strong anisotropy of fracture between the two loading directions is noted, which is attributed to the manufacturing defects. Conventional and optimized heat treatments exhibit high yield and ultimate strengths while the ductility is significantly improved. This is due to a new optimization of the process parameters allowing drastic reduction of the number of defects. These two heat treatments enable now a choice of the morphology of the grains between columnar or equiaxial as a function of the type of loading.
921 citations
TL;DR: In this paper, the microstructural properties of advanced high strength and supra-ductile TRIP and TWIP steels with high-manganese concentrations (15 to 25 mass%) and additions of aluminum and silicon (2 to 4mass%) were investigated as a function of temperature (−196 to 400°C) and strain rate (10−4≤e≤103 s−1).
Abstract: The microstructural properties of advanced high strength and supra-ductile TRIP and TWIP steels with high-manganese concentrations (15 to 25 mass%) and additions of aluminum and silicon (2 to 4mass%) were investigated as a function of temperature (−196 to 400°C) and strain rate (10−4≤e≤103 s−1). Multiple martensitic γfcc (austenie)→ehcpMs (hcp-martensite)→αbccMs (bcc-martensite)-transformations occurred in the TRIP steel when deformed at higher strain rates and ambient temperatures. This mechanism leads to a pronounced strain hardening and high tensile strength (>1 000 MPa) with improved elongations to failure of >50%. The austenitic TWIP steel reveals extensive twin formation when deformed below 150°C at low and high strain rates. Under these conditions extremely high tensile ductility (>80%) and energy absorption is achieved and no brittle fracture transition temperature occurs. The governing microstructural parameter is the stacking fault energy Γfcc of the fcc austenite and the phase stability determined by the Gibbs free energy ΔGγ→e. These factors are strongly influenced by the manganese content and additions of aluminum and silicon.The stacking fault energy Γfcc and the Gibbs free energy G were calculated using the regular solution model. The results show that aluminum increases Γfcc and suppresses the γfcc→ehcpMs transformation, whereas silicon sustains the γfcc→ehcpMs transformation and decreases the stacking fault energy. At the critical value of Γfcc≈25 mJ/mol and for ΔGγ→e>0, the twinning mechanism is favored. At lower stacking fault energy of (Γfcc 0, martensitic phase transformation will be the governing deformation mechanism.The excellent ductility and the enhanced impact properties enable complex deep drawing or stretch forming operations of sheets and the fabrication of crash absorbing frame structures.
893 citations
TL;DR: In this article, the effect of build orientation, layer thickness and feed rate on the mechanical performance of PLA samples manufactured with a low-cost 3D printer is investigated, where tensile and three-point bending tests are carried out to determine the mechanical response of the printed specimens.
877 citations
TL;DR: Friction stir welding (FSW) was used to weld 7075 T651 aluminum, an alloy considered essentially unweldable by fusion processes as discussed by the authors, which exposed the alloy to a short time, high-temperature spike, while introducing extensive localized deformation.
Abstract: Friction stir welding (FSW), a new welding technique invented at TWI, was used to weld 7075 T651 aluminum, an alloy considered essentially unweldable by fusion processes. This weld process exposed the alloy to a short time, high-temperature spike, while introducing extensive localized deformation. Studies were performed on these solid-state welds to determine mechanical properties both in the longitudinal direction, i.e., within the weld nugget, and, more conventionally, transverse to the weld direction. Because of the unique weld procedure, a fully recrystallized fine grain weld nugget was developed. In addition, proximate to the nugget, both a thermomechanically affected zone (TMAZ) and heat affected zone (HAZ) were created. During welding, temperatures remained below the melting point and, as such, no cast or resolidification microstructure was developed. However, within the weld nugget, a banded microstructure that influences room-temperature fracture behavior was created. In the as-welded condition, weld nugget strength decreased, while ductility remained high. A low-temperature aging treatment failed to fully restore T651 strength and significantly reduced tensile ductility. Samples tested transverse to the weld direction failed in the HAZ, where coarsened precipitates caused localized softening. Subsequent low-temperature aging further reduced average strain to failure without affecting strength. Although reductions in strength and ductility were observed, in comparison to other weld processes, FSW offers considerable potential for welding 7075 T651 aluminum.
864 citations
TL;DR: The "work-hardening" capability and ductility of this class of metallic glass is attributed to a unique structure correlated with atomic-scale inhomogeneity, leading to an inherent capability of extensive shear band formation, interactions, and multiplication of shear bands.
Abstract: Usually, monolithic bulk metallic glasses undergo inhomogeneous plastic deformation and exhibit poor ductility (< 1%) at room temperature. We present a new class of bulk metallic glass, which exhibits high strength of up to 2265 MPa together with extensive "work hardening" and large ductility of 18%. Significant increase in the flow stress was observed during deformation. The "work-hardening" capability and ductility of this class of metallic glass is attributed to a unique structure correlated with atomic-scale inhomogeneity, leading to an inherent capability of extensive shear band formation, interactions, and multiplication of shear bands.
863 citations