Simultaneous Improvement Of Strength Research Articles

Mechanical Behavior of Novel Suction Cast Ti-Cu-Fe-Co-Ni High Entropy Alloys

The present investigation reports mechanical properties of novel multicomponent TixCuyFe20Co20Ni20 high entropy alloys (HEAs) with different alloy chemistry (x/y = 1/3, 3/7, 3/5, 9/11, 1, 11/9 and 3/2). The alloy cylinders were prepared by vacuum arc melting-cum-suction casting route. The detailed electron microscopic observations reveal the presence of three different solid solution phases; FCC (a1) phase, FCC (a2) phase and BCC (b) phase for all the investigated alloys, whereas ultrafine eutectic between FCC (a1) phase, and Ti2 (Co, Ni) - type Laves phase has been observed for the HEAs with x/y = 9/11, 1, 11/9 and 3/2. Room temperature compression test of the suction cast cylinders with aspect ratio of 2/1 has been conducted to obtain mechanical properties of the HEAs. The optimum combination of strength (~ 1.88 GPa) and plasticity (~ 21 %) is obtained for x/y = 9/11; indicating simultaneous improvement of strength as well as plasticity of the novel HEAs. Fractographic analysis of the fractured surfaces reveals mixed mode of fracture for x/y = 1/3, 3/7 and 3/5, ductile mode for x/y = 9/11 and 1, whereas brittle mode of fracture for x/y = 11/9 and 3/2.

Enhancement in Strength and Ductility of Al-Mg-Si Alloy by Cryorolling followed by Warm Rolling

The effect of cryorolling followed by warm rolling (CR+WR) on strength and ductility of Al- Mg-Si alloys has been studied in the present work. Ultrafine grained Al 6063 alloy was developed through cryorolling up to 80% and warm rolling up to 50% at 200°C followed by ageing at 100°C for 22 hr. It is compared with the material processed through cryorolling followed by low temperature ageing. By implementing this new approach, simultaneous improvement in strength (290MPa) and ductility (15%) was achieved in Al 6063 alloys. The microstructure and precipitate evolution were characterized by Optical microscope, Electron back scattered diffraction (EBSD) and Transmission electron microscope (TEM) techniques. The ultrafine grain structure with 150-300nm was observed in CR+WR sample. Mechanical properties were studied by performing hardness and tensile testing at room temperature. Strength and ductility of CR+WR samples are found to be superior to CR sample after peak ageing treatment.

Tensile Behavior of Ultrafine-Grained Al-4Zn-2Mg Alloy Produced by Cryorolling

An Al-4Zn-2Mg alloy was subjected to cryorolling (CR) followed by short annealing. An average grain size of ~100 nm was achieved. Cryorolled samples showed large reduction in grain size due to suppression of dynamic recovery and absence of annihilation of dislocations, as compared to room temperature rolled samples. Further, the ultrafine-grained (UFG) Al-4Zn-2Mg alloy when subjected to natural aging showed an improved strength of ~413 MPa with ductility of ~25%, as compared to ~360 MPa and 22% ductility in peak aged condition of coarse-grained alloy. However, UFG alloy in peak aging condition, exhibited a relatively strength (~375 MPa) and 24% ductility combinations than the natural aging condition. The latter is attributed to dynamic precipitation and stored energy. In the present study, it is demonstrated that simultaneous improvement in strength as well as ductility can be achieved for the Al-4Zn-2Mg alloy through CR and controlled heat treatment combinations.

Green fabrication of chitosan films reinforced with parallel aligned graphene oxide

The excellent water solubility of graphene oxide (GO) imparts it feasibility as a new filler for reinforcing hydrophilic biopolymers. In this work, we present a simple and green approach to fabrication of GO/chitosan nanocomposite films. Mechanical properties of the nanocomposite have been significantly enhanced without sacrificing the optical transparency. GO sheets are unidirectionally aligned in the chitosan matrix and parallel to the surface of nanaocomposite film, which has been manifested by the morphological observation and explained by the theoretical prediction of tensile modulus. With incorporation of 1 wt% GO, the fracture strength and tensile modulus of the nanocomopsites are significantly enhanced by 93% and 51%, respectively. The simultaneous improvement of strength and toughness could be attributed to the homogeneous dispersion and alignment of GO sheets in the chitosan matrix, the strong interfacial adhesion between GO and chitosan, as well as the high specific surface area and the two-dimensional geometry of GO.

Application of spinodal decomposition to produce metallic glass matrix composite with simultaneous improvement of strength and plasticity

An original two-step procedure, based on the miscibility gap between two elements, produced an in-situ bulk metallic glass matrix composite. The Zr-Ta binary alloy, which exhibits a large immiscible region in solid state, formed a two-phase mixture of Zr- and Ta-rich solid solution by phase separation. When the Zr-Ta binary alloy was remelted with Cu, Zr, and Ti, the Ta-rich solid solution, which has a high melting temperature, did not melt, while the remaining melt containing Zr-rich solid solution mixed with the other elements and solidified into an amorphous phase at lower temperatures. The improvement of strength in the composite indicates that the interfaces between the Ta-rich particles and the BMG matrix formed by phase separation are strong enough to hold a high interfacial cohesion strength.

Simultaneous improvement of strength and ductility of Al–Mg–Si alloys by combining equal-channel angular extrusion with subsequent high-temperature short-time aging

The aging behaviour after room temperature (RT) equal-channel angular extrusion (ECAE) of the pre-ECAE solid-solution treated 6060 Al alloy was investigated in wide ranges of temperature, time, and ECAE pre-strain. It is shown that high-temperature, short-time aging is most effective in improving both strength and ductility. Compared to the commercially available peak aged condition with coarse grains, an increase of ∼35% in both ultimate tensile strength and uniform elongation was obtained after one extrusion and aging at 170 °C for 18 min. Competing recovery and precipitation activity play a significant role in enhancing the ductility of Al–Mg–Si alloys. This work demonstrates a strategy for an efficient processing of UFG Al alloys with outstanding mechanical properties.

Simultaneous improvement of strength and ductility in NiAl–Cr(Mo)–Hf near eutectic alloy by small amount of Ti alloying addition

Effects of Ti alloying addition on the microstructure and room temperature compression deformation behavior of a NiAl–Cr(Mo)–Hf near eutectic alloy were investigated by SEM, TEM, EDX and compression test. The results showed that compared with base alloy, the compressive fracture strain and 0.2% yield strength of the Ti-containing alloy were enhanced simultaneously. Disordered (Ti,Hf) solid solution phase together with the blocky Heusler phase Ni 2Al(Ti,Hf) precipitation presented at eutectic cell boundaries is responsible for the enhancement in ductility due to the better deformation ability of (Ti,Hf) solid solution phase. The improvement in strength depends mainly on the solid solution strengthening in NiAl matrix by large amount of Ti due to its larger solid solubility relative to Hf in NiAl.

Doping-induced simultaneous improvement of strength and ductility in ultrafine grained gold wires

The room temperature tensile properties of ultrafine-grained 25-μm gold wires were evaluated as a function of calcium (Ca) doping at various strain rates ranging between 10−3 and 10−1 s−1. Paradoxically, the increased amount of Ca was found to simultaneously increase the strength and ductility of the Au wires. However, based on scanning electron microscopy and tensile characterization, the grain size distributions, strain-hardening rate, and strain rate sensitivity of Au wires did not change with Ca, thus showing that neither grain refinement nor plastic instability are likely to be responsible for the concurrent improvement of strength and ductility.

Role of nanometer-scale quasicrystals in improving the mechanical behavior of Ti-based bulk metallic glasses

The effect of the precipitation of nanosized quasicrystals on the mechanical properties of Ti–Zr–Cu–Ni–Be bulk metallic glasses (BMG) has been investigated. The Ti40Zr29Cu8Ni7Be16 BMG crystallizes by forming a few nanometer-size quasicrystals in the amorphous matrix, enabling the fabrication of quasicrystal-reinforced BMG matrix composites. Simultaneous improvement of strength and ductility can be obtained when 3–5-nm-size quasicrystals are isolated and homogeneously distributed in an amorphous matrix. The fracture strength and global strain, respectively, increase from 1921 MPa and 5.1% for as-cast BMG to 2084 MPa and 6.2% for partially crystallized BMG with the volume fraction of ∼7% quasicrystals. These improvements may be attributed to the structural similarity between quasicrystalline and amorphous phases. Stable low-energy interface between two phases may act as a source for multiple-shear-band formation.

Fracture toughness correlation with microstructure and other mechanical properties in near-eutectoid steel

The variation of yield strength and fracture toughness was investigated for four different heat treatments attempted on specimens of a near-eutectoid steel. The aim of this study was to optimize the microstructure for simultaneous improvements in strength and toughness. Further, the fracture toughness deduced through empirical relations from tensile and charpy impact tests was compared with those measured directly according to ASTM Designation: E 399. Among the four different heat treatments attempted in this study, the plane strain condition was valid in the fracture toughness tests for (i) normalized and (ii) hardened and tempered (500°C for 1 h) treatments only. The latter of the two heat treatments resulted in simultaneous improvement of strength and plane strain fracture toughness. The finely-dispersed carbides seem to arrest the crack propagation and also increase the strength. The pearlitic microstructure of the former leads to easy crack propagation along cementite platelets and/or cementite/ferrite interfaces. The nature of variation of empirically determined toughness values from tensile tests for different heat treatments is similar to that measured directly through fracture toughness tests, although the two sets of values do not match quantitatively. On the other hand, the toughness data deduced from charpy impact test is in close agreement with that evaluated directly from fracture toughness tests.

The effect of TiO 2 addition on strengthening and toughening in intragranular type of 12Ce-TZP/Al 2O 3 nanocomposites

To compensate the definite disadvantages of lower strength and lower hardness in Ce-TZP, an intragranular type of 12Ce-TZP/0–30 vol% Al 2O 3 nanocomposite was investigated. Furthermore, the effect of TiO 2 addition on strengthening and toughening was also examined for the optimum component of 30 vol% Al 2O 3, which showed a maximum strength of 866 MPa. For these composites, a novel interpenetrated intragranular microstructure was presented, in which either 200-nm-sized Al 2O 3 particles or 30–50-nm-sized ZrO 2 particles were trapped within the ZrO 2 grains or Al 2O 3 grains, respectively. The TiO 2 was confirmed to dissolve into the tetragonal ZrO 2 lattice, and contributed to the phase stability of the tetragonal phase and the promotion of intragranular nano-dispersion. For the small amount (0.2 mol%) of TiO 2 doped 12Ce-TZP/30 vol% Al 2O 3 composite, simultaneous improvements in strength (1012 MPa) and toughness ( 10.2 MPa · m 1 2 for the IF method, 5.7 MPa · m 1 2 for the SEVNB method) were achieved through tailoring the sintering condition.

セラミックスのケミカルプロセッシング 新しい相互ナノ複合化コンセプトの構築と強靭性ジルコニア系複合焼結体の設計

To develop a new attractive ceramic material in which both high strength and high toughness might be achieved, we have established the new concept of an interpenetrated intragranular nanostructure based on the general design of the nanocomposites. The composite system designed according to the above concept possesses a novel microstructural feature. That is, for the composite composing of A and B phases, either nanometer sized A particles or equivalent sized B particles locate within the micron sized B grains or A grains, respectively. By applying the above material design, we succeeded to achieve a simultaneous improvements in strength and toughness for both Y-TZP and Ce-TZP based composite systems. This progress breaks through the strength-toughness tradeoff relation essentially existing in transformation toughened zirconia and its composite materials. In this paper, realized interpenetrated intragranular nanostructure along with forming process and mechanical properties will be described.

Microstructure and mechanical behaviour of 3Y-TZP/Mo nanocomposites possessing a novel interpenetrated intragranular microstructure

Yttria stabilized tetragonal zirconia polycrystal (Y-TZP)/0-100 vol % molybdenum (Mo) composites were fabricated by hot-pressing a mixture of Y-TZP powder containing 3 mol % yttria (Y2O3) and a fine Mo powder in vacuum. This composite system possessed a novel microstructural feature composed of an interpenetrated intragranular nanostructure, in which either nanometer sized Mo particles or equivalent sized zirconia (ZrO2) particles located within the ZrO2 grains or Mo grains, respectively. The strength and toughness were both greatly enhanced with increasing Mo content for the 3Y-TZP/Mo composites thus breaking through the strength-toughness tradeoff relation in transformation toughened ZrO2 and its composite materials. They exhibited a maximum strength of 2100 MPa and a toughness of 11.4 MPa·m1/2 for the composite containing 70 vol % Mo. These simultaneous improvements in strength and toughness were determined to be the result of a decrease in flaw size associated with the interpenetrated intragranular nanostructure, and a stress shielding effect created in the crack tip by the elongated Mo polycrystals bridging the crack tip in addition to the stress induced phase transformation.

A new type of nanocomposite in tetragonal zirconia polycrystal-molybdenum system

A ceramic/metal nanocomposite in tetragonal zirconia-molybdenum system possesses a novel microstructural feature composed of a mutual intragranular nanostructure, in which either nanometer sized Mo particles or equivalent sized zirconia particles are located within the zirconia grains or Mo grains, respectively. It achieves a simultaneous improvement in strength and toughness that overcomes the strength-toughness tradeoff relation.

Effects of Widmanstätten ferrite on the mechanical properties of a 0.2 pct C-0.7 pct Mn steel

Laboratory melted and rolled C-Mn steel plates were austenitized at either 925 °C or 1150 °C to produce nominal austenite grain sizes of 60 and 200 µm, resspectively. The plates were then cooled at rates in the range of about 2 °C/min to 400 °C/min to produce mixed polygonal ferrite/Widmanstatten ferrite/pearlite microstructures. The percentage of WidmanstAtten structure (a Widmanstatten ferrite/pearlite aggregate) increases with increasing prior austenite grain size and cooling rate. Both yield strength and impact toughness increase with decreasing austenite grain size and increasing cooling rate. This simultaneous improvement in strength and toughness is attributed to overall refinement of both the polygonal ferrite and WidmanstAtten structure. Both yield and tensile strength increase with an increase in the volume fraction of WidmanstAtten ferrite and a reduction in ferrite grain size. In contrast, the toughness level achieved in these polygonal ferrite/WidmanstAtten ferrite/pearlite microstructures depends largely on the ferrite grain size; the finer the grain size, the better the toughness.

Ｙ２Ｏ３安定化正方晶ジルコニア／金属ナノ複合材料の微構造と機械的特性

Yttria stabilized tetragonal zirconia polycrystal (Y-TZP)/0-100 vol% molybdenum (Mo) composites were fabricated by hot-pressing a mixture of Y-TZP powder containing 3mol% yttria and a fine Mo powder in vacuum. This composite system possessed a novel microstructural feature composed of a mutual intragranular nanostructure, in which either nanometer sized Mo particles or equivalent sized zirconia particles were located within the zirconia grains or Mo grains, respectively. Both fracture strength and toughness increased with increasing Mo content. They achieved a simultaneous improvement in strength and toughness that overcame the strength-toughness tradeoff relation. A maximum fracture strength of 2100 MPa was obtained at 70 vol% Mo content. Moreover, a fracture toughness increased dramatically with increasing Mo content above 40 vol% and exhibited 18.0 MPa⋅m 1/2at above 50 vol% Mo content. The relation between microstructure and mechanical properties will be discussed.

Rupture strength of structural steels after thermomechanical treatment

1. A significant improvement in the set of in-service properties of the commercially smelted ferritic-pearlitic steels under investigation is achieved as a result of TMT in the intercritical temperature interval (regulated rolling at 800°C) and accelerated cooling; this is associated with the formation of mixed ferritic-martensitic and ferritic-bainitic-martensitic structures, which ensure a simultaneous improvement in strength, plasticity, impact strength, cold resistance, and crack resistance (fracture toughness). 2. Even a negligible change in the alloying system of monotypic ferritic-pearlitic structural steels (an increase in carbon content from 0.15 to 0.18% and alloying with 0.2% of Mo in lieu of 0.33% of Cu) leads to a significant change in the character of the fine crystalline structure during TMT in the intercritical temperature interval, and, consequently, to a different degree of hardening and resistance to brittle fracture for this class of steels.

A qualitative model for the development of tough ceramics

A qualitative working model is presented in this paper for the development of tough ceramics. The model shows that toughness can be imparted only to dispersed multiphase ceramics in preference to single phase ceramics. A simultaneous improvement in strength can be achieved by securing a strong bond between the dispersed phase and the matrix. Eutectic composites of mixed oxides merit serious consideration as potential tough ceramics.