Different Amounts Of Deformation Research Articles

Matrix effect on strengthening behavior of carbon nanotubes in aluminum matrix composites

Many studies have shown that carbon nanotubes (CNTs) have excellent strengthening effect as a reinforcement in pure aluminum (Al). However, it is unknown that whether such merit can be also achieved in strong Al alloys for achieving higher-strength Al matrix composites. In this study, CNTs were incorporated into pure Al and a high-strength Al alloy (AA5083) via the same powder metallurgy route. Results showed that during the dispersion stage, the high energy ball milling process caused different amounts of deformation to pure Al and AA5083, which led to a better dispersion state of CNTs in powders and composites of pure Al. Although the two composites had the same tensile strength coincidentally, the reinforcing effect of CNTs in pure Al composite was more than five folds larger than that in AA5083, suggesting a strong matrix effect on strengthening behavior of CNTs in Al matrix composites. The present finding may show significant guidance for the optimization of fabrication processes and development of high-performance CNTs/Al composites. • Strengthening behavior of CNTs/pure Al and CNTs/AA5083 composites were compared. • The dispersion states of CNTs in the CNTs/pure Al and CNTs/AA5083 composites were compared especially. • The reinforcing efficiency of CNTs under poor dispersion state and fine dispersion state in two different matrices were discussed.

Microstructure Evolution and Mechanical Properties of Heterogeneous Nano/Ultrafine‐Grained Austenitic Stainless Steel Prepared by Low‐Temperature Rolling and Annealing

An 18Cr–8Ni austenitic stainless steel is subjected to cold rolling at room temperature and low temperature (−50 °C) under different amounts of deformation. The samples cold rolled to 70% deformation are then annealed to obtain nano/ultrafine‐grained steels with a good strength–ductility combination. The effects of cold rolling temperature and deformation amount on the microstructure evolution of austenitic stainless steel during rolling are investigated. The results reveal that low‐temperature rolling reduces the stacking fault energy of austenitic stainless steel and promotes the formation of shear bands, ε‐martensite, and α′‐martensite. For both low‐temperature and room‐temperature rolling, the austenite and α′‐martensite, austenite and ε‐martensite, α′‐martensite and ε‐martensite pairs follow the Kurdjumov–Sachs (K–S), Shoji–Nishiyama (S–N), and Burgers orientation relationships, respectively. The deformation‐induced martensite transformation sequence of austenitic stainless steel follows the processes γ → α' and γ → ε → α'. A heterogeneous nano/ultrafine‐grained structure with a grain size of 560 nm is obtained by low‐temperature rolling and annealing; room‐temperature rolling achieves a grain size of 690 nm. The heterogeneous nano/ultrafine‐grained steel exhibits a high yield strength of 908 MPa and maintains a satisfactory total elongation of 43%.

Initial Deformation Behaviors in Lean Duplex Stainless Steel

The deformation behaviors of the austenite phase in lean duplex stainless steels were investigated through uniaxial tension tests with different amounts of deformation. Microstructural analysis showed that in the initial deformation stage the deformation in austenite grains had a predominant effect on the strain hardening behavior of the LDX-2101 steel. The initial deformation in the austenite grains was found to be mainly accommodated by the formation of stacking faults. As the deformation increased further, mechanical twins were generated by the initial stacking faults and sequentially interacted with dislocations to accommodate the strain. The analysis of dislocation behavior revealed that the deformation twinning process followed the three-layer twin formation mechanism.

Effect of rolling with different amounts of deformation on microstructure and mechanical properties of the Mg–1Al–4Y alloy

In this study, the Mg–1Al–4Y alloy was successfully prepared by smelting and casting. Then, the alloy was rolled at different amounts of deformation (40%, 60%, and 80%) at 500 °C. Microstructure observations were carried out by X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). The effects of different amounts of rolling deformation on the microstructure and mechanical properties of Mg–1Al–4Y alloy were investigated. The results indicate that in the as-cast Mg–1Al–4Y alloy, the Al2Y phase is dispersed in the magnesium matrix, and the grain size of the alloy decreases from 201.06 μm to 35.07 μm with increasing rolling deformation. The rolled Mg–1Al–4Y alloy has a strong {0001} basal texture. As the amount of rolling deformation increases, the texture intensity gradually increases, but the texture type does not change substantially. Moreover, the Mg–1Al–4Y alloy is prone to {101¯2} extension twinning, {101¯1} contraction twinning, and {101¯1}-{101¯2} double twinning during rolling. Compared with the as-cast Mg–1Al–4Y alloy, the tensile strength and yield strength of the Mg–1Al–4Y alloy after 80% deformation were as high as 257 MPa (104%) and 185 MPa (an increase of 330%).

An effective method to obtain Cu-35Zn alloy with a good combination of strength and ductility through cryogenic rolling

In the present study, commercial Cu-35Zn α-brass sheets were subjected to cryogenic rolling (CR) to obtain samples with different amounts of deformation in the thickness direction. A self-designed liquid nitrogen cooling system that can simultaneously cool the work rollers and samples was used to ensure an ultra-low temperature condition during the rolling process. The grains, deformation twins, and dislocation density of the samples were studied by optical microscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD). Uniaxial tensile tests and Vickers hardness measurements were conducted to measure the mechanical properties of the samples. The microstructures and mechanical properties of CR samples were apparently improved compared to the room temperature rolling (RTR) samples with increasing deformation amount. As a typical example, when the deformation amount is 90%, the CR sample possesses ultrafine microstructures and demonstrates extraordinary mechanical properties. The average tensile and yield strengths of a 90% deformation CR sample can be improved to 835.3MPa and 711.5MPa, while those of a 90% deformation RTR sample are 718.6MPa and 481.2MPa. The average elongation of the CR sample is 2.9%, which is acceptable compared with the RTR sample whose average elongation is 3.1%. The ultrafine microstructures containing ultrafine grains, high density dislocation, and nanometer scale deformation twins in the 90% deformation CR sample may be the main reason for its extraordinary mechanical properties. Therefore, samples with a good combination of strength and ductility were obtained in the present study. This may be a valuable exploration to fabricate Cu-35Zn alloy sheets with excellent microstructures and mechanical properties.

Influence of Si and Ge Microalloying Additions and Plastic Deformation on Precipitation Processes in Al-Cu Based Alloys

The combined effect of micro-alloying with Si and Ge and/or plastic deformation prior to ageing at 160°C on age hardening has been studied in an Al-2 at% Cu alloy. The results obtained indicate that the hardness response is faster and the peak hardness is higher when plastic deformation and micro-alloying are applied together than performing each procedure individually. Different amounts of deformation, ranging from 0% to 30% have been utilized. An optimum deformation degree for the hardening response has been established around 8% for the Al-Cu-Si-Ge alloy. Characterization by transmission electron microscopy (TEM) shows that the peak hardness is due to a complex microstructure that contained θ" disc shaped precipitates, rod-shaped Si-Ge precipitates and θ' plates that were heterogeneously nucleated on the Si-Ge particles. Pre-deformation has been found to stimulate the growth of the θ' plates due to enhanced diffusion along dislocation cores. Increasing deformation reduces the influence of the Si-Ge precipitates on heterogeneous nucleation, leading to reduced peak hardness and faster over-ageing.

Microstructural anisotropy of ferritic ODS alloys after different production routes

Concepts for future generation fusion reactors have demanding requirements for the structural materials. High neutron doses and elevated temperatures form a harsh environment in which present commercially available materials cannot be used. A new class of oxide dispersion strengthened (ODS-) materials which are currently being developed have a high chance of meeting these requirements.The application of ODS steels as functional or structural application strongly depends on the availability of large batches of materials. Since no commercial ODS-alloys are available at the moment, investigations on large scale batches are crucial for future applications.The effects of powder particle size distribution on the microstructural properties were studied by scanning electron microscopy with electron backscatter diffraction. Although a homogeneous and fine grain size distribution was achieved after rolling, areas with different amounts of deformation were found. Microstructural properties and anisotropy effects are correlated to Charpy-impact tests. The materials after rolling shows a DBBT well below −50°C with excellent impact energies. Detailed investigations on the crystallographic textures concluded the work.

Effect of compression deformation on the microstructure and corrosion behavior of magnesium alloys

The effect of deformation on the corrosion and mechanical behavior of wrought Mg-alloys AZ31, AM50, and ZK60 was investigated. The materials’ behavior was correlated to the changes in metallurgical features, during compression, into different amounts of deformation at three temperatures: 250°C, 280°C, and 350°C. The metallurgical features were monitored by optical microscope, scanning electron microscope (SEM), and transmission electron microscopy (TEM). It was observed that there is a very strong correlation between three features: 1. metallurgical features (mainly twinning, dislocation accumulation, and dynamic recrystallization); 2. The thermo-mechanical state (amount of deformation and its temperature); and 3. The corrosion behavior of wrought Mg-alloys. This correlation was emphasized by the mechanical behavior measured through micro-hardness. Microstructural changes during deformation, and potentio-dynamic corrosion tests were correlated. These results show that studies on the effect of thermo-mechanical state (related to the microstructure) on the corrosion behavior of wrought Mg-alloys are essential in order to optimize their applicability to plastic forming processes.

Characterization of Precipitation Kinetics of Inconel 718 Superalloy by the Stress Relaxation Technique

Inconel 718 is a nickel-chromium-iron superalloy which presents excellent mechanical properties at high temperatures, as well as good corrosion resistance and weldability. These characteristics can be optimized with an appropriate control of microstructural features such as grain size and precipitation. Precipitates of different nature can form in these alloys, i.e. γ’’ (a metastable metallic compound Ni3Nb), γ’ (Ni3(Ti, Al), carbides and/or δ phase (intermetallic Ni3Nb). Aging treatments are usually designed to obtain the precipitation required in order to optimize mechanical properties. However, precipitation can also appear induced by deformation and therefore interfere with hot forming operations, such as forging. Under these conditions, precipitation may lead to an increase of the loads required to carry out the process. The aim of the work was the characterization of precipitation kinetics for Inconel 718. With this purpose, stress relaxation tests were carried out at temperatures ranging from 950°C to 800°C. Moreover, different amounts of deformation were applied to the samples, prior to stress relaxation, to evaluate the effect of this variable on inducing precipitation. Some samples were quenched at different relaxation times for metallographic evaluation. The results obtained through mechanical testing, together with a proper characterization of precipitation by Scanning Electron Microscopy, were the basis for obtaining precipitation-time-temperature (PTT) diagrams after different deformation conditions.

Microstructure evolution and strain localization in Cu and Cu‐8Al single crystals subjected to channel‐die compression

Single crystals of pure Cu and Cu-8%Al with two initial orientations, {112}111 and {112}110, were subjected to monotonic compression in channel-die at room temperature (293 K). The dislocation microstructure and local crystallography were investigated by transmission electron microscopy after different amounts of deformation. Various factors, such as initial single crystal orientation, chemical composition and amount of plastic deformation, were analysed in order to determine their influence on the microstructure evolution, local orientation variations and strain localization phenomena.

Surface roughness changes on a hot-dipped galvanized sheet steel during deformation at low strain levels

During a study on surface roughening as a function of deformation, an anomalous behavior of the surface roughening for hot-dipped galvanized sheet steel was observed during low levels of imposed strain. A mechanistic model, which explains this surface roughening behavior, is presented. Surface topography parameters, including surface roughness, and relative zinc crystal orientation data, were measured after different amounts of deformation were imposed on the sheet. The proposed model is consistent with both sets of data. The model indicates that the zinc crystals on the surface of the coated sheet steel will initially deform by twinning, which causes a slight increase in surface roughness. The twin regions of the zinc crystals are then favorably oriented for dislocation glide, and the roughness during further deformation will slightly decrease. Once the zinc crystal orientations have homogenized, standard surface roughening due to adjacent grain constraint occurs. Further evidence to support the model include: (1) Twinning in a single crystal of zinc causes a roughness increase of the same magnitude as that found in the zinc coated steel after low strain deformation, (2) twinning of zinc has been observed in other studies of zinc-coated sheet steels, and (3) discontinuous yielding of the steel and recrystallization of the zinc during the sheet deformation did not occur and are not the cause for both the surface roughness and crystal orientation results.

Evolution of microstructures during dynamic recrystallization and dynamic recovery in hot deformed Nimonic 80a

Dynamic recrystallization and dynamic recovery were investigated in a hot deformed nickel based superalloy, Nimonic 80a, for different amounts of deformation and strain rates of 0.1, 1.0 and 5.0 s −1. The area fraction of dynamic recrystallization was determined and micro-hardness was measured in different regions within the deformed grains. Dislocation structures were examined using transmission electron microscopy and dislocation density was determined by X-ray line broadening analysis. Micro-hardness is generally higher at grain boundaries near dynamically recrystallized grains. The overall dislocation density is highest for the intermediate strain rate of 1.0 s −1, which is consistent with variances of the average micro-hardness. This experimental observation is ascribed to dynamic strain aging of the alloy.

Strength and fracture of two hot-rolled Ti–Al–Si–Nb dual phase alloys based on Ti 3Al

Ti–Al–Si–Nb dual phase alloys are mainly composed of α 2-Ti 3Al matrix and Ti 5Si 3 silicide phases. In this paper, two alloys (402 and 405) whose Si contents are 2 and 5 at% respectively were arc melted and hot-rolled into sheets with different amounts of deformation. The silicide phase (Ti,Nb) 5(Si,Al) 3 was broken up into small pieces and redistributed in the α 2 matrix during the hot-rolling. Improved strength and ductility of the two alloys were observed after hot-rolling, which can be attributed to both the finely distributed reinforcement silicide phase and refinement of the matrix grain size. The mechanical properties of the two alloys are dependent on their volume fractions of the silicide phase: the strength of alloy 405 is higher than that of alloy 402, while alloy 402 is more ductile than alloy 405. The brittle–ductile transition temperature of the two dual phase alloys is between 600 and 800°C. The surface slip on the dual phase alloys was also observed. Obvious separation between the (Ti,Nb) 5(Si,Al) 3 particles and the α 2 matrix is found on the fracture surfaces obtained at high temperature, showing dimple-like morphology.

Scaling of Misorientation Angle Distributions

The measurement of misorientation angle distributions following different amounts of deformation in cold-rolled aluminum and nickel and compressed stainless steel is reported. The scaling of the dislocation cell boundary misorientation angle distributions is studied. Surprisingly, the distributions for the small to large strain regimes for aluminum, 304L stainless steel, nickel, and copper (taken from the literature) appear to be identical. Hence the distributions may be ``universal.'' These results have significant implications for the development of dislocation based deformation models.

Rock Glaciers of the Dalton Range, Kluane Ranges, South-West Yukon Territory, Canada

AbstractGlaciated valleys of the Dalton Range in the south-west Yukon Territory are dominated by rock glaciers identified as glacier ice-cored debris systems. The two rock glaciers studied have different amounts of deformation at present, resulting from post-formation mechanics.The primary formation of lobes of the rock glaciers resulted from periods of glacier activity in the Neoglacial, although older lobes, probably late Pleistocene in age, occur below the Neoglacial lobes. The hydrological systems of the rock glaciers have played a major role in the post-formation deformation of the land forms and the present drainage system is entirely sub-surface. The explanation for the extensive occurrence of rock glaciers in the Dalton Range is lithological as a result of the high susceptibility of the Upper Jurassic/Lower Cretaceous sediments to frost action and glacier erosion.

Rock Glaciers of the Dalton Range, Kluane Ranges, South-West Yukon Territory, Canada

Abstract Glaciated valleys of the Dalton Range in the south-west Yukon Territory are dominated by rock glaciers identified as glacier ice-cored debris systems. The two rock glaciers studied have different amounts of deformation at present, resulting from post-formation mechanics. The primary formation of lobes of the rock glaciers resulted from periods of glacier activity in the Neoglacial, although older lobes, probably late Pleistocene in age, occur below the Neoglacial lobes. The hydrological systems of the rock glaciers have played a major role in the post-formation deformation of the land forms and the present drainage system is entirely sub-surface. The explanation for the extensive occurrence of rock glaciers in the Dalton Range is lithological as a result of the high susceptibility of the Upper Jurassic/Lower Cretaceous sediments to frost action and glacier erosion.