Microhardness Behavior Research Articles

Mechanical properties of electrodeposited amorphous/crystalline multilayer structures in the Fe-P system

Amorphous/crystalline multilayer structures of Fe-P alloys were deposited electrochemically using the single bath technique. Hall-Petch behavior of microhardness with respect to sublayer thickness was observed down to a sublayer thickness of 15nm. For thinner sublayers, a hardness plateau was obtained. The transition at a sublayer thickness of 15nm coincides with the loss of the multilayer structure as observed in transmission electron microscopy. The transition is a possible result of a change in the amorphous to crystalline sublayer thickness ratio and the interface roughness development during the deposition process. Additionally, crack deflection at the interfaces was observed for the layered structures with small sublayer thickness in microbending experiments.

Microhardness and corrosion resistance behaviour of Ti–6Al–4V alloy‐coloured surface under WEDM‐HS process

In this work, the reaction films were generated on the Ti–6Al–4V alloy by means of high-speed wire electrical discharge machining (WEDM-HS) technology in order to improve its microhardness and corrosion resistance. The microhardness was evaluated by using a nanoindentation tester. The corrosion behaviour was studied using measurements of potentiodynamic polarisation and electrochemical impedance spectroscopy. The experimental results showed that the processed alloys presented a higher microhardness than the matrix, and the thicker film on the surface had a greater microhardness. Additionally, the corrosion resistances of the processed alloys were superior, which could have been due to the lower corrosion current densities and the higher impedance values. Furthermore, the corrosion current densities of the processed alloys would decrease with thicker reaction films. This research provides important insights into the surface modification of titanium alloys.

Elevated electrochemical corrosion behavior of a B4C/Al neutron absorber by shot peening modification

AbstractThe shot peening (SP) method was employed to modify the surface properties of 33% B4C/Al composites. The microhardness, morphology, and corrosion behavior of B4C/Al composites were characterized by using the Vickers hardness test, scanning electron microscopy, potential dynamic scanning, and electrochemical impedance spectroscopy. The experimental observations revealed that the B4C particles were embedded into the matrix, which rendered the plastic deformation of Al alloy near the surface of B4C/Al composites on the condition of the high-speed impact of projectiles. As such, the density and hardness of the B4C/Al composite modified layer near the surface were enhanced. After the SP treatment, the results of the electrochemical polarization curve test showed that the corrosion potential increased by 55.2 mV, the corrosion current changed from 3.828×10-6 to 1.102×10-6 A/cm2, and the corrosion rate decreased by 72.2%, respectively. This indicates that the corrosion resistance significantly improved via the SP treatment. The mechanism of the formation of Al alloy modified layer and electrochemical corrosion behaviors is discussed in detail.

Effects on hardness and microstructure of AISI 1020 low-carbon steel processed by high-pressure torsion

Low-carbon steel AISI 1020 was subjected to high-pressure torsion (HPT) with 6.0GPa pressure through 1/4–5 turns. The microstructures of the samples in each turn were studied by means of X-ray diffraction (XRD) analyzing the changes in micro-strain, crystallite size and lattice parameter. Vickers testing was utilized to study the microhardness behavior of the samples subjected to HPT processing. The morphology evolution of the samples and especially the changes in ferrite and pearlite structures were studied for different numbers of turns using scanning electron microscopy (SEM).

Impact of Applied Potential on the Structural and Non-lubricated Wear Composite Coating in Petrochemical Industry

The need to improve the structural properties of materials in petrochemical industry, due to recurring failure, has motivated this study. The effect of deposition potential on structural integrity, surface topography and micromechanical progression of Zn based induced aluminium and TiO2 alloy coating series on mild steel was studied. The wear stability and microhardness behaviour of the developed composite coating was examined via, respectively, sliding reciprocating rig and dura scan diamond based microhardness tester. The structural reliability was inspected with scanning electron microscope equipped with EDS, and atomic force microscope. The results showed that the superb structural crystal resulted into a significant increase in the microhardness, and into a decrease in wear plastic deformation in a non-lubricated system. The precipitation of the deposits enforces stable crystal orientation and compact grains growth. The work has established that up to 13wt% TiO2 on zinc rich bath, a solid composite coating on mild steel, can be used to improve the service life of coating for stable structural properties.

Sintering of dental ceramic/sol–gel-derived bioactive glass mixtures for dental applications: the study of microstructural, biological, and thermal properties

Although dental ceramic restorations are biocompatible, they are not necessarily bioactive. They can be modified by bioactive glasses to exhibit bioactive behavior well adapted to the surrounded tissue. Such modification can be done using mixtures of dental ceramic/sol–gel-derived bioactive glass expected to prolong the life time of the fixed dental prosthesis by preventing the formation of secondary caries. In the current study, these mixtures with different compositions were sintered in the laboratory in order to simulate the oral condition in which the restoration is used. Biological behavior was evaluated by immersion of the specimens in simulated body fluid. The microstructural and thermal properties of the sintered specimens were studied using X-ray diffractometry, Fourier transform infrared spectroscopy, field emission scanning electron microscopy/energy dispersive spectroscopy and dilatometry. One of the mixtures was used as a layering material on the dental ceramic, and its attachment to the substrate, fracture surface, micro-hardness, and bioactivity behavior was evaluated. Sintering enhanced the crystallinity of the mixtures and they exhibited a good bioactive behavior. In addition, applying one of the mixtures as coating on ceramic substrate was a successful process in which the product revealed acceptable properties.

Mechanical Behaviour of Gas Nitrided Ti6Al4V Bars Produced by Selective Laser Melting

Gas atomized Ti-6Al-4V (Ti64) alloy powder was used to prepare distinct designed geometries with different properties by selective laser melting (SLM). Several heat treatments were investigated to find suitable processing parameters to strengthen (specially to harden) these parts for different applications. The results showed significant differences between tabulated results for heat treated billet Ti64 and SLM produced Ti64 parts, while certain mechanical properties of SLM Ti64 parts could be improved by different heat treatments using different processing parameters. Most heat treatments performed followed the trends of a reduction in tensile strength while improving ductility compared with untreated SLM Ti64 parts.Gas nitriding [GN] (diffusion-based thermo-chemical treatment) has been combined with a selected heat treatment for interstitial hardening. Heat treatment was performed below β-transus temperature using minimum flow of nitrogen gas with a controlled low pressure. The surface of the SLM produced Ti64 parts after gas nitriding showed TiN and Ti2N phases (“compound layer”, XRD analysis) and α (N) – Ti diffusion zones as well as high values of micro-hardness as compared to untreated SLM produced Ti64 parts. The microhardness profiles on cross section of the gas nitrided SLM produced samples gave information about the i) microhardness behaviour of the material, and ii) thickness of the nitrided layer, which was investigated using energy dispersive spectroscopy (EDS) and x-ray elemental analysis. Tensile properties of the gas nitrided Ti64 bars produced by SLM under different conditions were also reported.

Sliding wear performance of nickel-based cermet coatings composed of WC and Al2O3 nanosized particles

Abstract This paper investigates the sliding wear performance of two types of co-electrodeposited cermet coatings composed of nano-sized tungsten carbide (WC) and combined tungsten carbide and alumina (Al2O3) particles incorporated in a nickel matrix. For this purpose, the effects of alternating the ceramic particle concentration in the electrolyte solutions on microhardness of the coatings and also the effect of applied loads on wear performance of the coatings have been studied using ball-on-flat sliding wear tests. The wear track volumes and the progression of wear depths as a function of time and at three applied loads were recorded and wear track morphologies were investigated using FE-SEM and microhardness testing. The results showed that microstructure, microhardness and wear performance of the coatings composed of WC improved when Al2O3 particles were introduced into the matrix. It was also found that the rule of mixtures for composite materials provides a good explanation for microhardness behaviour while Archard equation can explain the changes in wear performance due to the hardness and microstructural changes.

Phase stabilization of plasma-sprayed alumina coatings by spraying mechanically blended alumina–chromia powders

ABSTRACTA study of phase stabilization is performed on atmospheric plasma-sprayed alumina–chromia coating applied on low-carbon steel substrates. Alumina–chromia mixture with varying amounts of chromia content (1 wt.% to 6 wt.%) is used for this purpose. X-ray diffraction (XRD) analysis is carried out to investigate the different phase compositions of the coatings. Quantification of the different phases present in the coatings is performed by subsequent use of Rietveld refinement method. Surface morphology, microhardness, and wear behavior of the different coatings are also observed. Rietveld analyses performed on coatings ensure the stabilization of metastable phases present in the alumina coatings by chromia addition. Significant increase of the α -alumina and (AlxCr1-x)2O3 content is observed in alumina coatings with 4 wt.% chromia content. This is supported by the improved hardness and wear-resistant properties of the alumina coatings containing 4 wt.% chromia. The minimum surface roughness of the coating is also observed for alumina coatings with 4 wt.% chromia content among all the alumina coatings with different chromia content. The formation of alumina–chromia solid solution and solidification of α-alumina are found to be the reasons behind the enhancement in mechanical properties of the coating.

Microstructure and deformation behaviour of laser welded dissimilar dual phase steel joints

The microstructure, microhardness, tensile properties, deformation and fracture behaviour of the Nd:YAG laser welded dissimilar joints between 780 and 980 MPa dual phase steels over a wide strain rate range were investigated. The welded joint shows hardening in fusion zone, supercritical and intercritical heat affected zones and softening in subcritical heat affected zones. For the dissimilar welded joint, the changing trend of the ductility is similar to those of the base metals with respect to the strain rate. The reason for the strain rate sensitivity of the failure location of the welded joint is that the major factor influencing the failure location changes from the content of ferrite to the content of ferrite/martensite interface with increasing strain rate.

Dry Sliding Wear and Corrosion Behaviour of Al-Based Hybrid Composites Reinforced with Micro-Tip and Micro/Nano-Al2O3p

The commercially pure Al matrix composites reinforced with micro-Ti (Ti) particles as well as micro-Al2O3 (MA) or nano-Al2O3 (NA) particles have been developed via powder metallurgy route. Detailed microstructural characterizations as well as evaluation of microhardness, wear and corrosion behaviour have been carried out. As a basis for comparison, the same has also been investigated for the Al composites reinforced with these particles alone (i.e., Ti, MA, NA). The hybrid composites (i.e., Al + Ti + MA and Al + Ti + NA) reinforced with two different types of particles (i.e., Ti + MA/NA) have been found to exhibit relatively better hardness response; higher wear resistance and inferior response to corrosion, as compared to the composites (Al + Ti, Al + MA and Al + NA) reinforced with these particle alone.

Effects of 1,2-dichloroethane on the optical, thermal, mechanical and NLO behaviors of ADP crystals

The effects of 1,2-Dichloroethane (DCE) over a concentration range from 1 to 5mol% on the optical absorption, hardness, thermal, microhardness behaviors and SHG efficiency of ammonium dihydrogen phosphate (ADP) single crystals grown by slow evaporation solution growth technique have been investigated. The powder X-ray diffraction and FT-IR analyses indicate that the crystals undergo considerable stress as a result of doping and these also confirm the slight distortion of the structure of the crystal in the presence of a high concentration of dopant (5mol%). UV–vis studies reveal that the absorption of the DCE doped crystals is less than that of pure ADP. Thermal studies (TG/DTG) disclose that the decomposition temperature of doped ADP is more than that of pure ADP. Vicker's microhardness study reveals that the addition of DCE increases the hardness of the ADP. SHG efficiency of DCE doped ADP is higher than that of pure ADP. Presence of dopant was confirmed by energy-dispersive spectrometry.

Influence of Pd Addition of CoCrMo Biomedical Alloys on the Microhardness Behaviour

Influence of Pd Addition of CoCrMo Biomedical Alloys on the Microhardness Behaviour

Effect of alumina and silicon carbide hybrid reinforcements on tensile, compressive and microhardness behavior of Mg–3Al–1Zn alloy

Powder metallurgy method was used to synthesize Mg–3Al–1Zn-(1.5Al2O3–xSiC) composites, to investigate the influence of Al2O3 and SiC hybrid particles on mechanical properties of magnesium alloy. The mechanical characterization of as-extruded composites demonstrated enhanced 0.2% yield strength, and ultimate strength, and reduced fracture strain (Strain at fracture) values both in tension and compression loading. The micro hardness (Vickers hardness, Hv) of composites was increased with increasing reinforcement particle contents. The mechanical characterization of heat treated samples indicated the enhanced fracture strains and reduced microhardness, 0.2% tensile yield strength, ultimate tensile strength. The enhanced fracture strains of heat treated sample are attributed to the dissolved Mg17Al12 intermetallic phases in the matrix. An attempt is made to narrate the effect of heat treatment, presence of Al2O3 and SiC hybrid particles, and their increasing amount on microstructural and mechanical properties of magnesium alloy.

INFLUENCE OF MICROSTRUCTURE OF FRICTION STIR WELDED JOINTS ON GROWTH AND PROPERTIES OF MICROARC OXIDATION COATINGS ON AZ31B MAGNESIUM ALLOY

Ceramic coatings on friction stir welded (FSW) joints of AZ31B magnesium alloy were fabricated by microarc oxidation (MAO) method in silicate electrolyte. Microstructure, phase constituents, microhardness and electrochemical corrosion behaviors of bare and coated magnesium alloys at different zones of FSW joints for different oxidation time were investigated. The influence of microstructure at different zones on the growth of MAO coatings was analyzed. The results show that the MAO coatings on FSW joints are uniform, and they have almost the same morphology, phase constituents, hardness and corrosion resistance at base metal, stir zone and heat-affected zone. The properties of MAO coatings are independent on the microstructures of AZ31B alloy. In addition, the microstructures of magnesium alloy near the coating/alloy interface at different zones of FSW joint was not changed by microarc discharge process.

A Performance Study of Clinched Joints with Local Thermal Treatment

In order to investigate the influence of local thermal treatment to microstructure and static mechanical behavior on clinched joints of cold rolling steel (SPCC) . The clinched joint performed local thermal treatment based on the test platform, and successively adopting metallographic, micro-hardness and static mechanics behavior test. The result show that the microstructure of SPCC clinching joints found a large amount of lath martensite after quenching treatment, and in comparison to which without local thermal treatment, its static strength is enhanced by 45.39% and its hardness increased by 77.78% .

Effect of Microstructure on Properties of NiCrBSi Alloys Applied by Flame-Powder Deposition

This article deals with studying the relationships among the chemical composition, microstructure and properties (hardness, micro-hardness, wear resistance) of powder additives based on NiCrBSi after their deposition. Tested materials reached a relatively wide range of hardness after deposition, which corresponds to their chemical composition and microstructure. The abrasive wear resistance of materials was tested on an emery cloth. The results indicate that both the hardness and abrasive wear resistance of tested materials depend especially on the content of carbon and chromium. Microstructural analysis indicates that the structure of tested materials is formed by the γ-Ni solid solution and intermediate phases based on boron, silicon and carbon. Those mostly form eutectics (three types), or are excluded by precipitation. There was also found a significant effect of chromium, but especially carbon content on the ratio between the solid solution and eutectics in the microstructure of tested materials. These different ratios of solid solution and eutectics were markedly reflected in micro-hardness behaviours in deposited layers. Micro-hardness values confirmed also the presence of carbidic particles in the layers with carbon content higher than 0.7 wt%.

Effect of microstructure of vacuum-deposited Fe100−xNix (30 < x < 39) foils with FCC structure on their mechanical properties

The present paper considers the relation between microstructure characteristics of vacuum-deposited Fe100−xNix (30<x<39) foils and their mechanical properties. The foils 40–100μm thick with various microstructure characteristics were prepared using electron beam physical vapor deposition (EBPVD) onto substrates maintained at different temperatures in the 250–700°С range. The foil microhardness increases as deposition temperature decreases and reaches the maximum value of 5GPa for foils deposited at 300°C. It has been shown that the crystallite size in the foils decreases monotonically from sub-micron values (over 100nm) to nanoscaled ones (10–20nm), while the level of microstrains of FCC lattice increases to 1% with lowering deposition temperature. The dependence of foil microhardness on the crystallite size in the Hall–Petch’s coordinates (Hμ vs d−1/2) exhibits the deviation from a linear function at microhardness of 5GPa. Such behavior of the foil microhardness at decreasing deposition temperature correlates with an abrupt increase in both porosity and microstrains level.

High temperature corrosion behaviour of wire arc sprayed Fe based coatings

Fe–Cr–Al and Fe–Cr–Al–B cored wires were designed and produced to deposit protective coatings for components used in high temperature environments by wire arc spraying technique. The microstructure, microhardness and high temperature corrosion behaviour of the new coatings were investigated in comparison with Fe–Cr coating and with commercial Fe–Cr–Al coating. All coatings presented lamellar microstructures with oxide inclusions. The new Fe–Cr–Al–B coating showed the fewest oxide inclusions among all the coatings. The microhardness of Fe–Cr–Al coating was quite low, while the microhardness of Fe–Cr–Al–B was found to be higher. Thermogravimetric analysis was used to evaluate the high temperature corrosion behaviour of the coatings in a molten salt (Na2SO4–25%K2SO4) environment at 650°C under cyclic conditions. The results showed that the new Fe–Cr–Al–B coating exhibited the best high temperature corrosion behaviour.

Electrodeposition and mechanical property of Ni–Co–ZrC coatings

In order to improve the mechanical properties of Ni–Co coating, Ni–Co–ZrC composite coatings were electrodeposited from a modified Watts bath. Surface morphology, composition and microstructure of the coatings were characterised by scanning electron microscopy, energy dispersive spectrometer and X-ray diffraction analysis. Mechanical properties of the coatings including microhardness and tribological behaviour were investigated by Vicker microhardness tester and tribotester. Ni–Co and Ni–Co–ZrC coatings all exhibited anomalous deposition behaviour. By increasing the Co content, surface morphology of the coatings was changed from nodular structure to branched morphology and the dominant phase was changed from fcc Ni to hcp Co. Compared with Ni–Co coatings, Ni–Co–ZrC coatings possessed smaller grain size and exhibited better mechanical properties. Phase composition, grain size and ZrC particles content of the coatings were applied to explain the evolution of the morphology, microstructure and mechanical properties of the coatings. Among the coatings, Ni-Co-ZrC coating with 43 at-% Co exhibits the highest microhardness and the Ni-Co-ZrC coating with the highest Co content exhibits the best tribological behaviour.