Effect of Cr addition on microstructures and nanohardness of rapidly solidified Ti–48Al alloy

Abstract

In this present work, the microstructure and nanohardness of rapidly solidified Ti–48 at-%Al alloy with various Cr additions were experimentally investigated using the single roller melt spinning technique. Ti–48Al alloy with various Cr additions were prepared by arc melting for comparison. In the arc melted alloy, the volume fraction of the interdendritic γ phase decreases, and the lamellar structure and the B2 phase increase with the increase in Cr addition. After rapid solidification, the Ti–48Al alloy consists of the γ phase and α₂ the phase, with the γ phase as the matrix. The α₂ phase exists as particles or in lamellar structure, which embed in the matrix. With 2 at-%Cr addition, the alloy ribbons mainly consist of equiaxial α₂ grains and small particles of the B2 phase, with few lamellar structures occasionally found at the triple grain boundary. Increasing Cr content to 4 at-%, the grain size of the B2 phase increases, and lamellar structures disappear. The change in nanohardness was discussed based on the microstructural observations. It shows a certain increase in the nanohardness as Cr content increases to 4 at-%. This can be attributed to the changes in the microstructures.     

Characterization and Properties of Layered Silicate Reinforced Spent DuraForm EX Nanocomposites

During the last decade, the nanocomposites based on layered silicate are widely studied and attracted the industrial and academic research. The effect of various loading levels of layered silicate reinforcement on the mechanical and thermal properties was studied by nano-indentation, flexural testing, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The maximum hardness (H), increased from 67 MPa for neat Spent DuraForm EX up to 170 MPa with 7 wt.% layered silicate-reinforced sample. The measured modulus (E), of unreinforced Spent DuraForm increased from 631 MPa to 2100 MPa with 7 wt.% layered silicate reinforcement. The thermal property of the EX nanocomposites revealed by DSC was improved by about 6?C up to 7 wt.% of layered silicate loading. Different levels of layered silicates dispersion as characterized using TEM and SEM correlated strongly with improvements in nanohardness and thermal properties. The improved hardness, modulus, crystalline and melting temperatures of Spent DuraForm EX nanocomposites are attributed mainly to the intercalated structures.     

Properties of ZnO coatings obtained by mechanoactivated oxidation

In this work a new method based on the mechanoactivated oxidation has been applied for obtaining thin nanostructured transparent ZnO coatings on glass. Zn has been transferred onto a glass substrate at room temperature using a quickly rotating steel wire brush. Afterwards by subsequent annealing it is modified into a transparent ZnO coating. The temperature range in which formation of the needle-like (whiskers) structure and transition to the fine-grained structure occurs has been determined. The interrelation between physical properties and the change of microstructure of the ZnO coatings has been shown.     

Anomalies in Hall-Petch strengthening for nanocrystalline Au-Cu alloys below 10 nm grain size

The mechanical behavior of an electrodeposited nanocrystalline alloy is assessed with regards to the experimentally measured strain-rate sensitivity. Foils are characterized with grain sizes as small as 3 nm, a nano-scale regime that has previously gone without detailed experimental examination. It is found from micro-scratch measurements that hardness, hence strength, approaches ideal values as the grain size decreases to 7 nm. Below 7 nm, softening in strength and departure from Hall-Petch behavior is related to an increase in the activation volume for deformation as grain size decreases further.     

Influence of loading rate on nanohardness of sapphire

This work reports the loading rate effect on nanohardness of sapphire. The intrinsic nanoscale contact deformation resistance of sapphire increased with the loading rates following empirical power law dependence with a positive exponent. The results showed a significant enhancement (e.g., ~66%) of the nanohardness of sapphire with the increase in loading rates from 10 to 10,000 μN s⁻¹. These results were explained mainly in terms of the maximum shear stress generated underneath the nanoindenter, dislocation density and critical resolved shear stress of the sapphire.     

Nanomechanical properties of friction stir welded AA6082-T6 aluminum alloy

Lightweight alloys are of major concern, due to their functionality and applications in transport and industry applications. Friction stir welding (FSW) is a solid-state welding process for joining aluminum and other metallic alloys and has been employed in aerospace, rail, automotive and marine industries. Compared to the conventional welding techniques, FSW produces joints which do not exhibit defects caused by melting. The objective of the present study is to investigate the surface hardness (H) and elastic modulus (E) in friction stir welded aluminum alloy AA6082-T6. The findings of the present study reveal that the welding process softens the material, since the weld nugget is the region where the most deformations are recorded (dynamic recrystallization, production of an extremely fine, equiaxial structure), confirmed by optical microscopy and reduced nanomechanical properties in the welding zone. A yield-type pop-in occurs upon low loading and represents the start of phase transformation, which is monitored through a gradual slope change of the load-displacement curve. Significant pile-up is recorded during nanoindentation of the alloy through SPM imaging.     

Revealing heterogeneous C partitioning in a medium Mn steel by nanoindentation

The present work employs nano-indentation technique to investigate the C partitioning in a medium Mn steel subjected to quenching and tempering process. It is found that the C partitioning between martensite and austenite is inhomogeneous. Particularly, the large lenticular martensite has negligible C partitioning into the austenitic matrix as it maintains an ultra-high nanohardness comparable to the one without tempering. Strategies to suppress the formation of large martensite are discussed.     

Anisotropy in nanohardness of microplasma sprayed hydroxyapatite coating

Abstract

Abstract

In the present paper, the authors report the observation of pronounced nanohardness anisotropy in a phase pure, 230?μm thick microplasma sprayed bioactive hydroxyapatite coating on a surgical grade SS316L substrate. The coating had a very heterogeneous microstructure with a large number of macrocracks, microcracks, inter- and intrasplat cracks, intra- and interlamellar macro- and micropores, etc. The nanohardness values measured by the nanoindentation technique at various loads in the range 10-1000?mN on cross-section was usually higher than those measured on plan-section of the coating. This anisotropy of nanohardness could be attributed to the larger volume per cent porosity as well as higher spatial density of planar defects, pores and cracks on plan-section over those in the cross-section. In addition, the dependence of hardness on porosity of hydroxyapatite was studied in detail.     

Effect of in-situ oxidation on the nanomechanical evolution of Fe-base coating with ceramic particles produced by internal rotating plasma spraying

In this work, we investigated FeCrMo coatings with 35 wt% ceramic, which were produced on a cylinder surface by an internal rotating plasma spraying and oxidized in air. The ceramic particles consisted of 80 wt% alumina and 20 wt% zirconia, which can improve the mechanical properties of the coating. For microstructural characterization, scanning electron microscopy was combined with energy dispersive X-ray analysis and electron probe micro analysis, and the nanomechanical properties were measured by a nanoindentation tester. The structure of Fe-base coating matrix consists of Al₂O₃, ZrO₂ and a small amount of mixed Fe–Cr oxides, and the ceramic particles exhibit a uniform distribution. During oxidation, a mixed oxide layer containing Fe₂O₃ and Fe₃O₄ forms on the surface of the Fe-base coating, and the thickness of the oxide layer increases with increasing oxidation temperature. Due to the in-situ oxidation, the nanohardness and Young's modulus of the Fe-base coating decreased with increasing oxidation temperature. The nanohardness evolution of Fe-base coatings oxidized at different temperatures is discussed.     

Relationships between the fretting wear behavior and mechanical properties of thin carbon films

Mechanical load can drastically affect the properties of orthopedic implant materials. Damage of these materials usually occurs in contact surfaces, caused by abrasion, adhesion, fretting, delamination, pitting and fatigue depending on friction, lubrication, contact area, surface finish and level of loads (stresses).Carbon-based films are biocompatible with good bearing capacity, wear resistance, corrosion resistance and have a low coefficient of friction. However, great intrinsic stress prevents their wider application, mainly as implant coatings. To reduce this undesirable effect special deposition procedures are under development and/or the films are doped with suitable elements. It must be emphasized that DLC is not a material but a group of materials with a variety of properties. The relationships between the fretting wear behavior and mechanical properties of films based on carbon deposited by DC using the pulsed arc discharge PVD nitrogen doped (a-C) and the filtered pulsed arc discharge deposition system (ta-C) were tested.The composition of carbon films (sp³, sp²) was determined by Raman spectroscopy. Mechanical properties of elastic modulus and hardness were determined by a NanoTest apparatus with diamond Berkovich tip using the Oliver-Pharr procedure and adhesion was measured by nanoscratch tests. Tribological behavior was analyzed by fretting tests with a corundum ball under dry sliding lubricated conditions.The good performance of the hard carbon coatings is often discussed. Results from this study of fretting and the associated lubrication (bovine serum) show that ta-C coatings, despite their high hardness, have very low friction coefficients and low volume losses.