The influence of time, temperature, and grain size on indentation creep in high-purity nanocrystalline and ultrafine grain copper

2004 ◽  
Vol 85 (22) ◽  
pp. 5197-5199 ◽  
Author(s):  
Kai Zhang ◽  
J. R. Weertman ◽  
J. A. Eastman
Keyword(s):  
Grain Size ◽  
High Purity ◽  
Ultrafine Grain ◽  
Indentation Creep

High Strain Rate Deformation and Damage in Ceramic Materials

1993 ◽  
Vol 115 (3) ◽  
pp. 292-299 ◽  
Author(s):  
G. Raiser ◽  
R. J. Clifton
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
High Purity ◽  
Hot Pressing ◽  
Glassy Phase ◽  
Plane Waves ◽  
Weight Percent ◽  
Ultrafine Grain ◽  
Triple Junctions ◽  
Dynamic Tensile Strength

The objective of this investigation is to use a plate impact recovery experiment to identify the dominant failure mechanisms in conventional α-Al2O3 ceramics and thereby gain insight into the most promising, failure-resistant microstructures. A “soft-recovery” configuration is used wherein a star-shaped flyer impacts a square specimen. The impedances, shapes, thicknesses and orientation of all plates are designed to ensure a known history of longitudinal, planar stress waves throughout a central octagonal region of the specimen. The plane waves generated from this experiment are monitored by a laser interferometer system that allows data to be collected at four separate locations. The validity of the approach is demonstrated by a shot in which all plates were stressed within their elastic range. Subsequently, several experiments were conducted at nearly the same stress level with commercially sintered aluminas having different grain size and different glass content. These experiments, taken as a whole, demonstrate that improvement in alumina’s dynamic compressive properties is obtained by reducing the grain size. In compression, a reduction in grain size lowers average residual stresses at triple junctions and grain boundaries and makes the material less susceptible to inelastic deformation and sliding at triple junctions and grain boundaries. A reduction in the weight percent of pre-processing impurities (and therefore the amount of intergranular glassy phase) yields strong improvements in the dynamic tensile strength of the ceramic. A decrease in the amount of glassy phase tends to make tensile damage less likely by improving grain boundary strength. These trends were tested by conducting recovery experiments on a high-purity, small-grain alumina, processed in-house through hot pressing. Both the compressive resistance and, especially, the tensile resistance were superior to those found for all other tested specimens. The overall results suggest that the best failure resistance will be obtained for new, high-purity, ultrafine-grain ceramics that are prepared by hot pressing of nanometer scale powders.

scholarly journals Synthesis, microstructure, and properties of high purity Mo2TiAlC2 ceramics fabricated by spark plasma sintering

2020 ◽  
Vol 9 (6) ◽  
pp. 759-768
Author(s):  
Yunhui Niu ◽  
Shuai Fu ◽  
Kuibao Zhang ◽  
Bo Dai ◽  
Haibin Zhang ◽  
...  
Keyword(s):  
Grain Size ◽  
Flexural Strength ◽  
Spark Plasma Sintering ◽  
Layered Structure ◽  
High Purity ◽  
High Fracture Toughness ◽  
Temperature Range ◽  
Microstructure And Properties ◽  
Plasma Sintering ◽  
Spark Plasma

AbstractThe synthesis, microstructure, and properties of high purity dense bulk Mo2TiAlC2 ceramics were studied. High purity Mo2TiAlC2 powder was synthesized at 1873 K starting from Mo, Ti, Al, and graphite powders with a molar ratio of 2:1:1.25:2. The synthesis mechanism of Mo2TiAlC2 was explored by analyzing the compositions of samples sintered at different temperatures. It was found that the Mo2TiAlC2 phase was formed from the reaction among Mo3Al2C, Mo2C, TiC, and C. Dense Mo2TiAlC2 bulk sample was prepared by spark plasma sintering (SPS) at 1673 K under a pressure of 40 MPa. The relative density of the dense sample was 98.3%. The mean grain size was 3.5 μm in length and 1.5 μm in width. The typical layered structure could be clearly observed. The electrical conductivity of Mo2TiAlC2 ceramic measured at the temperature range of 2–300 K decreased from 0.95 × 106 to 0.77 × 106 Ω–1·m–1. Thermal conductivity measured at the temperature range of 300–1273 K decreased from 8.0 to 6.4 W·(m·K)–1. The thermal expansion coefficient (TEC) of Mo2TiAlC2 measured at the temperature of 350–1100 K was calculated as 9.0 × 10–6 K–1. Additionally, the layered structure and fine grain size benefited for excellent mechanical properties of low intrinsic Vickers hardness of 5.2 GPa, high flexural strength of 407.9 MPa, high fracture toughness of 6.5 MPa·m1/2, and high compressive strength of 1079 MPa. Even at the indentation load of 300 N, the residual flexural strength could hold 84% of the value of undamaged one, indicating remarkable damage tolerance. Furthermore, it was confirmed that Mo2TiAlC2 ceramic had a good oxidation resistance below 1200 K in the air.

scholarly journals Investigation of Polyol Process for the Synthesis of Highly Pure BiFeO3 Ovoid-Like Shape Nanostructured Powders

Nanomaterials ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 26 ◽  
Author(s):  
Manel Missaoui ◽  
Sandrine Coste ◽  
Maud Barré ◽  
Anthony Rousseau ◽  
Yaovi Gagou ◽  
...  
Keyword(s):  
Grain Size ◽  
Magnetic Properties ◽  
High Purity ◽  
Average Crystallite Size ◽  
Polyol Process ◽  
Pure Bifeo3 ◽  
Optimum Parameters ◽  
Mössbauer Measurements ◽  
Synthesis Protocol ◽  
Nanostructured Powders

Exclusive and unprecedented interest was accorded in this paper to the synthesis of BiFeO3 nanopowders by the polyol process. The synthesis protocol was explored and adjusted to control the purity and the grain size of the final product. The optimum parameters were carefully established and an average crystallite size of about 40 nm was obtained. XRD and Mössbauer measurements proved the high purity of the synthesized nanostructurated powders and confirmed the persistence of the rhombohedral R3c symmetry. The first studies on the magnetic properties show a noticeable widening of the hysteresis loop despite the remaining cycloidal magnetic structure, promoting the enhancement of the ferromagnetic order and consequently the magnetoelectric coupling compared to micrometric size powders.

scholarly journals Is Superplasticity in the Future of Nanophase Materials?

1990 ◽  
Vol 196 ◽  
Author(s):  
R. W. Siegel
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Room Temperature ◽  
Grain Boundary Sliding ◽  
Atomic Clusters ◽  
Diffusional Creep ◽  
Ultrafine Grain ◽  
Grain Sizes ◽  
Nanophase Materials ◽  
Boundary Sliding

ABSTRACTThe ultrafine grain sizes and high diffusivities in nanophase materials assembled from atomic clusters suggest that these materials may have a strong tendency toward superplastic mechanical behavior. Both small grain size and enhanced diffusivity can be expected to lead to increased diffusional creep rates as well as to a significantly greater propensity for grain boundary sliding. Recent mechanical properties measurements at room temperature on nanophase Cu, Pd, and TiO2, however, give no indications of superplasticity. Nonetheless, significant ductility has been clearly demonstrated in these studies of both nanophase ceramics and metals. The synthesis of cluster-assembled nanophase materials is described and the salient features of what is known of their structure and mechanical properties is reviewed. Finally, the answer to the question posed in the title is addressed.

Indentation Creep of Molybdenum: Comparison Between Thin Film and Bulk Material

1994 ◽  
Vol 356 ◽  
Author(s):  
K. B. Yoder ◽  
D. S. Stone ◽  
J. C. Lin ◽  
R. A. Hoffmann
Keyword(s):  
Thin Film ◽  
Grain Size ◽  
Room Temperature ◽  
Bulk Material ◽  
High Hardness ◽  
Rate Sensitivity ◽  
Indentation Creep ◽  
Creep Properties ◽  
Measurement Path ◽  
Arc Evaporation

AbstractIndentation creep, load relaxation, and rate-change experiments probe room temperature and 80°C creep properties of a 1.3 μm-thick molybdenum film on silicon. The film, with 0.51 GPa compressive stress, 8 GPa hardness and estimated 40 nm grain size, was deposited using steered-arc evaporation at -17V bias. Despite its small grain size and high hardness, the thin film behaves like bulk molybdenum does: the rate sensitivity of the hardness is only weakly-dependent on measurement path (as with bulk material), and activation volumes calculated based on strain rate sensitivity are consistent with those of bulk molybdenum We suspect deformation mechanisms are similar to those in bulk molybdenum under similar conditions.

scholarly journals Development of a Cr-Ni-V-N Medium Manganese Steel with Balanced Mechanical and Corrosion Properties

Metals ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 705 ◽  
Author(s):  
Tarek Allam ◽  
Xiaofei Guo ◽  
Simon Sevsek ◽  
Marta Lipińska-Chwałek ◽  
Atef Hamada ◽  
...  
Keyword(s):  
Grain Size ◽  
Stainless Steel ◽  
Corrosion Resistance ◽  
Twip Steel ◽  
Total Elongation ◽  
Manganese Steel ◽  
Ultrafine Grain ◽  
Corrosion Properties ◽  
Hot Rolled ◽  
20 Nm

A novel medium manganese (MMn) steel with additions of Cr (18%), Ni (5%), V (1%), and N (0.3%) was developed in order to provide an enhanced corrosion resistance along with a superior strength–ductility balance. The laboratory melted ingots were hot rolled, cold rolled, and finally annealed at 1000 °C for 3 min. The recrystallized single-phase austenitic microstructure consisted of ultrafine grains (~1.3 µm) with a substantial amount of Cr- and V-based precipitates in a bimodal particle size distribution (100–400 nm and <20 nm). The properties of the newly developed austenitic MMn steel X20CrNiMnVN18-5-10 were compared with the standard austenitic stainless steel X5CrNi18-8 and with the austenitic twinning-induced plasticity (TWIP) steel X60MnAl17-1. With a total elongation of 45%, the MMn steel showed an increase in yield strength by 300 MPa and in tensile strength by 150 MPa in comparison to both benchmark steels. No deformation twins were observed even after fracture for the MMn steel, which emphasizes the role of the grain size and precipitation-induced change in the austenite stability in controlling the deformation mechanism. The potentio-dynamic polarization measurements in 5% NaCl revealed a very low current density value of 7.2 × 10−4 mA/cm2 compared to that of TWIP steel X60MnAl17-1 of 8.2 × 10−3 mA/cm2, but it was relatively higher than that of stainless steel X5CrNi18-8 of 2.0 × 10−4 mA/cm2. This work demonstrates that the enhanced mechanical properties of the developed MMn steel are tailored by maintaining an ultrafine grain microstructure with a significant amount of nanoprecipitates, while the high corrosion resistance in 5% NaCl solution is attributed to the high Cr and N contents as well as to the ultrafine grain size.

Fracture Mechanics of Y2O3 Ceramics at High Temperatures

2014 ◽  
Vol 89 ◽  
pp. 88-93
Author(s):  
Marek Boniecki ◽  
Zdzislaw Librant ◽  
Władysław Wesołowski ◽  
Magdalena Gizowska ◽  
Marcin Osuchowski ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Grain Size ◽  
High Temperature ◽  
Fracture Mechanics ◽  
High Purity ◽  
Room Temperature ◽  
Bending Strength ◽  
Hot Isostatic Pressing ◽  
Temperature Changes ◽  
Four Point Bending

Fracture toughness KIc and four-point bending strength σc at high temperature (up to 1500 °C) of Y2O3 ceramics of various grain size were measured. The ceramics were prepared by pressureless air sintering and next hot isostatic pressing of high purity (99.99%) Y2O3 powder. Relative density of about 99 % was achieved. Photos of microstructures revealed small pores distributed mainly inside grains. For smallest grain size (2 - 9 μm) ceramics KIc and σc are almost constant from 20 ° to 1200 °C and next they decrease. For biggest grain size (about 44 μm) they increase up to 800 °C and next they keep constant up to 1200 °C. The micrographs analyses of fracture surfaces indicated that transgranular mode of fracture at room temperature changes to almost intergranular at higher temperatures.

The Effects of Free Space in Mould Cavity on Sandglass Extrusion

2005 ◽  
Vol 475-479 ◽  
pp. 2999-3002
Author(s):  
W.L. Lu ◽  
Y. Wang ◽  
Jin Tao Hai
Keyword(s):  
Grain Size ◽  
Free Space ◽  
Large Strain ◽  
Experimental Results ◽  
Experimental Result ◽  
Ultrafine Grain ◽  
Theory Analysis ◽  
Ultrafine Grain Size ◽  
Mould Cavity

Sandglass extrusion is an ultrafine grain size method. Due to the repetitive and multiple extrusions, large strain will be accumulated and ultafine grain size can be obtained. There are some factors that can affect the experimental result of sandglass extrusion. Among these factors, free space in mould cavity is very important, which can affect the forming of the fold during the extrusion. In this paper, the effects of free space in mould cavity on sandglass extrusion have been discussed and theory analysis and experimental results have been reported.

Fabrication of High Purity MgO Ceramic Targets by Hot-Isostatic Pressing

2017 ◽  
Vol 898 ◽  
pp. 1693-1698
Author(s):  
Miao Qin Chen ◽  
Jin Jiang He ◽  
Zhao Chong Ding ◽  
Xin He
Keyword(s):  
Grain Size ◽  
High Purity ◽  
Hot Isostatic Pressing ◽  
Average Particle Size ◽  
Growth Behavior ◽  
Average Particle ◽  
Average Grain Size ◽  
Grain Growth Behavior ◽  
Ceramic Targets ◽  
Hip Process

MgO ceramics with the purity higher than 99.99% have been fabricated by a hot-isostatic press (HIP) technique of hot-pressed MgO compacts using nanometer MgO powder with an average particle size of 300 nm. The densification and grain growth behavior of MgO compacts during HIP process were investigated. The results indicate that the high-purity MgO ceramic with an average grain size of 9.76 μm and a density approximately to the theoretical density can be obtained by HIP method at 1350°C and 150 MPa for 60 min. HIP can significantly enhance the densification process of MgO compacts and cause a slightly change of grain size distribution.

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