Research status of laser cladding on titanium and its alloys: A review

Corrosion fatigue of biomedical metallic alloys: Mechanisms and mitigation

In recent years innovation in carbon based materials have encouraged both researchers as well as industrialists to develop materials/composites with improved tribological properties Researchers have been fascinated to develop diamond like carbon (DLC) or carbon nanotubes (CNTs) reinforced coatings to their good corrosion resistance, excellent wear resistance, good adhesion strength, and self -lubricious nature The present review article is mainly focused on various techniques employed in order to process DLC/CNTs coatings as well as provide a summary of DLC/CNTs deposition on different substrates The present study includes major types, properties and tribological behavior of carbon based materials and mechanisms involved in coating deposition The study also discusses that deposition of DLC/CNTs coatings on the substrate materials enhances the wear, corrosion and mechanical properties of the substrate

A critical review of diamond like carbon coating for wear resistance applications

The effect of severe plastic deformation induced by multiple sliding impacts by the specimen surface produced at ultrasonic impact treatment (UIT) on the stress-controlled fatigue response of the powder metallurgy Ti–6Al–4V alloy is studied in this paper. Specimens of Ti–6Al–4V alloy were produced from Ti hydride precursor powders via the cost-effective blended elemental powder metallurgy technique. Structure investigations were performed by XRD, TEM, LM and SEM techniques. After UIT, fatigue strength was increased by about 60% on the base of 107 cycles, and lifetime was prolonged by two orders of magnitude at applied stress amplitudes of 300–400 MPa. The UIT process leads to approx. four times decrease in the surface roughness parameters. Increased by 65 and 20% microhardeness magnitudes are respectively registered on the top surface and on the depth of 100 μm. The UIT induced compressive stresses achieve about two thirds of the alloy yield stress. The hardness increase is shown to be coupled with the increased dislocation density, essentially refined of α+β microstructure and with randomization in α-grains orientations. Observations of cross-sections of the UIT processed specimens revealed the pores free near-surface layer of approx. 200 μm thick, which is formed thanks to micro-pore closure process promoted by high shear strains produced at the UIT induced sliding impacts. Analysis of fracture surfaces revealed subsurface cracks initiations and numerous fracture steps indicating on the cracks branching and deflection in the surface layers of the UIT processed specimens instead of superficial crack initiation and the grain boundary cleavages mainly observed in the pristine samples. Experimentally registered magnitudes of fatigue limit were successfully predicted by accounting for the effective stress intensity factor range ΔKth and observed by TEM microstructural units responsible for fatigue fracture (α-phase colonies, α-grains or micro-pores) and compared with literature data on PM Ti–6Al–4V alloy. Enhanced fatigue strength and prolonged lifetime of PM Ti–6Al–4V alloy after the UIT process are concluded to be associated with (i) minimized surface roughness; (ii) compressive residual stresses; (iii) UFG and nano-scale α+β microstructure; and (iv) micro-pore healing.

Enhanced fatigue behavior of powder metallurgy Ti–6Al–4V alloy by applying ultrasonic impact treatment

Corrosion evaluation of microarc oxidation coatings formed on 2024 aluminium alloy

The tendency of the aircraft industry is to enhance customer value by improving performance and reducing environmental impact. In view of availability, aluminum alloys have a historically tendency to faster insertion due to their lower manufacturing and operated production infrastructure. In landing gear components, wear and corrosion control of many components is accomplished by surface treatments of chrome electroplating on steel or anodizing of aluminum. One of the most interesting environmentally safer and cleaner alternatives for the replacement of hard chrome plating or anodizing is tungsten carbide thermal spray coating, applied by the high velocity oxy fuel (HVOF) process. However, it was observed that residual stresses originating from these coatings reduce the fatigue strength of a component. An effective process as shot peening treatment, considered to improve the fatigue strength, pushes the crack sources beneath the surface in most of medium and high cycle cases, due to the compressive residual stress field induced. The objective of this research is to evaluate a tungsten carbide cobalt (WC–Co) coating applied by the high velocity oxy fuel (HVOF) process, used to replace anodizing. Anodic films were grown on 7050-T7451 aluminum alloy by sulfuric acid anodizing, chromic acid anodizing and hard anodizing. The influence on axial fatigue strength of anodic films grown on the aluminum alloy surface is to degrade the stress-life performance of the base material. Three groups of specimens were prepared and tested in axial fatigue to obtain S–N curves: base material, base material coated by HVOF and base material shot peened and coated. Experimental results revealed increase in the fatigue strength of Al 7050-T7451 alloy associated with the WC 17% Co coating. On the other hand, a reduction in fatigue life occurred in the shot peened and coated condition. Scanning electron microscopy technique and optical microscopy were used to observe crack origin sites, thickness and coating/substrate adhesion.

Coating residual stress effects on fatigue performance of 7050-T7451 aluminum alloy

Fatigue behavior of PVD coated Ti-6Al-4V alloy

Effect of electroless nickel interlayer on the fatigue strength of chromium electroplated AISI 4340 steel

High strength/weight ratio and effective corrosion resistance are primary reasons to use titanium alloys replacing steel and aluminum in some aeronautical components. However, titanium alloys have poor tribological properties, which reduce devices performance under friction; making surface treatments a requirement to improve wear. Thermal spray coatings have attractive characteristics as high hardness and strong coating/substrate adhesion. Compared with thermal spray processes, the High Velocity Oxygen Fuel (HVOF) presents less porosity and oxide contents due to the lower flame temperature used in the process operation. Electroplated coatings used to improved abrasive wear and corrosion properties, affects negatively the fatigue strength, providing lower results than those for uncoated parts. To increase fatigue strength of coated materials, techniques as compressive residual stresses induced by shot peening are used. In this study the influence of WC–10%Co–4%Cr coating deposited by HVOF on the fatigue strength of Ti–6Al–4V alloy was evaluated. Comparison of fatigue strength of coated specimens and base material shows also a decrease when parts are coated. It was observed that the influence is more significant in high cycle fatigue tests. The shot peening prior to the thermal spray coating is an efficient surface treatment to improve fatigue resistance of coated Ti–6Al–4V. Scanning electron microscopy technique (SEM) was used to observe crack origin sites and thickness in all the coatings.

http://www.fem.unicamp.br/~giorgia/Costa%202009.pdf

Midori Yoshikawa Pitanga Costa

Papers

Coating residual stress effects on fatigue performance of 7050-T7451 aluminum alloy

Fatigue behavior of PVD coated Ti-6Al-4V alloy

Effect of electroless nickel interlayer on the fatigue strength of chromium electroplated AISI 4340 steel

Effect of WC-10%Co-4%Cr coating on the Ti-6Al-4V alloy fatigue strength

An investigation on sliding wear behavior of PVD coatings