A perspective of microplasma oxidation (MPO) and vapor deposition coatings in surface engineering of aluminum alloys

Over the past years, great achievements have been made in the development of coating technologies for surface improvement of aluminum alloys. Despite these achievements, the role in the market strongly depends on the ability of surface coating technology under technical and economic considerations to meet the increased demands for heavy tribological applications of aluminum alloys. Microplasma oxidation (MPO) technology has recently been studied as a novel and effective means to provide thick and hard ceramic coating with improved properties such as excellent load-bearing and wear resistance properties on aluminum alloys. The present work covers the evaluation of the performances of current single and duplex coatings combining MPO, physical vapor deposition (PVD), and plasma assisted chemical vapor deposition (PACVD) coatings on aluminum alloys. It suggests that the MPO coating is a promising candidate for design engineers to apply aluminum alloys to heavy load-bearing applications. The prospective future for the research on MPO coatings is introduced as well.

Characteristic Length of Metallic Nanorods under Physical Vapor Deposition

By using physical vapor deposition(PVD)to grow metallic nanorods,the characteristic length is controllable,which can be identified by two different growth modes:Mode I and Mode II.In Mode I,the growth of metallic nanorods is dominated by the monolayer surface steps.Whereas in Mode II,the growth mechanism is mainly determined by the multilayer surface steps.In this work,we focused on the analysis of the physical process of Mode I,in which the adatoms diffuse on the monolayer surface at beginning,then diffuse down to the next monolayer surface,and finally result in the metallic nanorods growth.Based on the physical process,both the variations of the characteristic length and the numerical solutions were theoretically proposed.In addition,the twodimensional(2 D)lattice kinetic Monte Carlo simulations were employed to verify the theoretical derivation of the metallic nanorods growth.Our results pay a new way for modifying the performance of metallic nanorods-based applications and devices.

High temperature tribological behaviour of PVD coated tool steel and aluminium under dry and lubricated conditions

Aluminium alloys are commonly used as lightweight materials in the automotive industry.This non-ferrous family of metallic alloys offers a high versatility of properties and designs.To reduce weight and improve safety,high strength-to-weight ratio alloys(e.g.6XXX and 7XXX),are increasingly implemented in vehicles.However,these alloys exhibit low formability and experience considerable springback during cold forming,and are therefore hot formed.During forming,severe adhesion(i.e.galling)of aluminium onto the die surface takes place.This phenomenon has a detrimental effect on the surface properties,geometrical tolerances of the formed parts and maintenance of the dies.The effect of surface engineering as well as lubricant chemistry on galling has not been sufficiently investigated.Diamond-like carbon(DLC)and CrN physical vapour deposition(PVD)coated steel have been studied to reduce aluminium transfer.However,the interaction between lubricants and PVD coatings during hot forming of aluminium alloys is not yet fully understood.The present study thus aims to characterise the high temperature tribological behaviour of selected PVD coatings and lubricants during sliding against aluminium alloy.The objectives are to first select promising lubricant-coating combinations and then to study their tribological response in a high-temperature reciprocating friction and wear tester.Dry and lubricated tests were carried out at 300℃ using a commercial polymer lubricant.Tests using DLC,CrN,CrTiN,and CrAIN coated tool steel were compared to uncoated tool steel reference tests.The initial and worn test specimen surfaces were analysed with a 3-dimensional(3D)optical profiler,scanning electron microscope(SEM)and energy dispersive X-ray spectroscope(EDS)as to understand the wear mechanisms.The results showed formation of tribolayers in the contact zone,reducing both friction and wear.The stability of these layers highly depends on both the coatings'roughness and chemical affinity towards aluminium.The DLC and CrN coatings combined with the polymer lubricant were the most effective in reducing aluminium transfer.

Microstructure inheritance of matrixes of SiC_(f)/Ti6242 composites from precursor wire coatings byα+βphase field consolidation

SiC_(f)/Ti composite owns the attractive advantages of lightweight and excellent high-temperature performance,which make it have great significance to the development of aerospace industry.However,the complicated fabrication route and novel architecture of SiC_(f)/Ti composite bring about more difficulties for controlling its microstructure.In this work,the method of regulating the structure and performance of the composite matrix by adjusting the characteristics of the precursor wire was explored.The physical vapor deposition(PVD)method was applied to fabricate precursor wires.Ti6242 coatings with bamboo leaf-shaped grains and chrysanthemumshaped grains were deposited on SiC fibers by changing the PVD condition.It is found that the original structure of the Ti6242 coating of precursor wire has significant impact on the microstructure of the composite matrix after hot isostatic pressing(HIP).The matrix transformed from the Ti6242 coating with bamboo leaf-shaped grains exhibits equiaxed grain structure.While the other matrix has a columnar crystal structure,and the inside of the columnar crystal inherits the original chrysanthemum-shaped structure.The columnar crystal matrix has lower hardness and modulus than the equiaxed grain matrix.

Growth of InGaN-based blue-LED on AlN/sapphire sputtered with different oxygen flow rate

Indium gallium nitride(InGaN)based blue light-emitting diodes(LEDs)suffer from insufficient crystal quality and serious efficiency droop in large forward current.In this paper,the InGaN-based blue LEDs are grown on sputtered aluminum nitride(AlN)films to improve the device light power and weaken the efficiency droop.The effects of oxygen flow rate on the sputtering of AlN films on sapphire and device performance of blue LEDs are studied in detail.The mechanism of external quantum efficiency improvement is related to the change of V-pits density in multiple quantum wells.The external quantum efficiency of 66%and 3-V operating voltage are measured at a 40-mA forward current of with the optimal oxygen flow rate of 4 SCCM.