Nanoindentation of nanocrystalline ZnO

A number of nanocrystalline ceramics have been fabricated by the gas phase condensation technique. The mechanical properties of one of the first ceramics produced by this method, nanophase TiO2, have been discussed in an earlier study.1 This paper reports a similar study undertaken to examine the properties of nanocrystalline ZnO. Nanoindenter techniques are used to determine hardness, Young's modulus, and strain rate sensitivity in ultra-fine grained ZnO. Significant properties variations are experienced within a given sample, indicating a large degree of microstructural inhomogeneity. Nevertheless, a distinct evolution in properties can be observed as a function of sintering temperature. Young's modulus and hardness values increase almost linearly with increasing sintering temperature, and, in addition, there also appears to be a linear correlation between the development of the two materials properties. In contrast, strain rate sensitivity is shown to have an inverse dependence on sintering temperature. This dependence appears to be linked to the strong influence of grain size on strain rate sensitivity, so that the lower sintering temperatures, which provide the finer grain sizes, tend to promote strain rate sensitivity. The results of this study are strikingly similar to those obtained earlier for nanophase TiO2, and they indicate that the earlier results could probably be generalized to a much broader range of nanocrystalline ceramics.

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Mechanical properties of nanophase TiO2 as determined by nanoindentation

Journal of Materials Research ◽

10.1557/jmr.1990.1073 ◽

1990 ◽

Vol 5 (5) ◽

pp. 1073-1082 ◽

Cited By ~ 304

Author(s):

M. J. Mayo ◽

R. W. Siegel ◽

A. Narayanasamy ◽

W. D. Nix

Keyword(s):

Strain Rate ◽

Single Crystal ◽

Young’S Modulus ◽

Strain Rate Sensitivity ◽

Sintering Temperature ◽

Young's Modulus ◽

Rate Sensitivity ◽

Ceramic Materials ◽

Microstructural Inhomogeneity ◽

Hardness Values

Nanoindenter techniques have been used to determine the hardness. Young's modulus, and strain rate sensitivity of nanophase TiO2, which is currently available only in very small quantities and which cannot be tested by most conventional techniques. Hardness and Young's modulus both increase linearly with sintering temperature over the range 25–900°C but come to within only 50–70% of the single crystal values. Strain rate sensitivity, on the other hand, is measurably greater for this material than for single crystal rutile, and the value of strain rate sensitivity increases as the grain size and the sintering temperature are decreased. In its as-compacted form, the strain rate sensitivity of nanophase TiO2 is approximately a quarter that of lead at room temperature, indicating a potential for significant ductility in these ceramic materials. Finally, a significant scatter in hardness values has been detected within individual nanophase samples. This is interpreted as arising from microstructural inhomogeneity in these materials.

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Effect of Consolidation and Sintering Parameters on the Mechanical Responses of Nanocrystalline Al-Fe Alloy Processed by Mechanical Alloying

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.719-720.87 ◽

2015 ◽

Vol 719-720 ◽

pp. 87-90

Author(s):

Muneer Baig ◽

Hany Rizk Ammar ◽

Asiful Hossain Seikh ◽

Mohammad Asif Alam ◽

Jabair Ali Mohammed

Keyword(s):

Mechanical Alloying ◽

Strain Rate ◽

Strain Rate Sensitivity ◽

Compressive Loading ◽

Rate Sensitivity ◽

Testing Temperature ◽

Fine Grained ◽

Mechanical Responses ◽

Wide Range ◽

High Frequency Induction

In this investigation, bulk ultra-fine grained and nanocrystalline Al-2 wt.% Fe alloy was produced by mechanical alloying (MA). The powder was mechanically milled in an attritor for 3 hours and yielded an average crystal size of ~63 nm. The consolidation and sintering was performed using a high frequency induction sintering (HFIS) machine at a constant pressure of 50 MPa. The prepared bulk samples were subjected to uniaxial compressive loading over wide range of strain rates for large deformation. To evaluate the effect of sintering conditions and testing temperature on the strain rate sensitivity, strain rate jump experiments were performed at high temperature. The strain rate sensitivity of the processed alloy increased with an increase in temperature. The density of the bulk samples were found to be between 95 to 97%. The average Vickers micro hardness was found to be 132 Hv0.1.

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Serration Flow Behavior with Abnormal Strain Rate Sensitivity of Fine-Grained Mg-0.8 Wt Pct Ca Alloy

Metallurgical and Materials Transactions A ◽

10.1007/s11661-013-1941-2 ◽

2013 ◽

Vol 44 (10) ◽

pp. 4469-4474 ◽

Cited By ~ 1

Author(s):

Qiuming Peng ◽

Hui Fu ◽

Wenlong Xiao

Keyword(s):

Strain Rate ◽

Strain Rate Sensitivity ◽

Flow Behavior ◽

Rate Sensitivity ◽

Fine Grained

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High-Temperature Deformation of Magnesium ElektronTM 43

Materials Science Forum ◽

10.4028/www.scientific.net/msf.735.93 ◽

2012 ◽

Vol 735 ◽

pp. 93-100

Author(s):

Alexander J. Carpenter ◽

Anthony J. Barnes ◽

Eric M. Taleff

Keyword(s):

Strain Rate ◽

Strain Rate Sensitivity ◽

Rate Sensitivity ◽

Superplastic Forming ◽

Solute Drag ◽

Grain Boundary Sliding ◽

High Temperature Deformation ◽

Temperature Deformation ◽

Fine Grained ◽

Boundary Sliding

Complex sheet metal components can be formed from lightweight aluminum and magnesium sheet alloys using superplastic forming technologies. Superplastic forming typically takes advantage of the high strain-rate sensitivity characteristic of grain-boundary-sliding (GBS) creep to obtain significant ductility at high temperatures. However, GBS creep requires fine-grained materials, which can be expensive and difficult to manufacture. An alternative is provided by materials that exhibit solute-drag (SD) creep, a mechanism that also produces elevated values of strain-rate sensitivity. SD creep typically operates at lower temperatures and faster strain rates than does GBS creep. Unlike GBS creep, solute-drag creep does not require a fine, stable grain size. Previous work by Boissière et al. suggested that the Mg-Y-Nd alloy, essentially WE43, deforms by SD creep at temperatures near 400°C. The present investigation examines both tensile and biaxial deformation behavior of ElektronTM 43 sheet, which has a composition similar to WE43, at temperatures ranging from 400 to 500°C. Data are presented that provide additional evidence for SD creep in Elektron 43 and demonstrate the remarkable degree of biaxial strain possible under this regime (>1000%). These results indicate an excellent potential for producing complex 3-D parts, via superplastic forming, using this particular heat-treatable Mg alloy.

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