Microstructure and wear resistance of in situ TiCp composite coating by laser cladding

A new in situ method was realized by one step laser cladding to produce Ni-base alloy composite coating reinforced by in situ reacted and gradiently distributed TiCp particles. The submicron TiCp particles were formed and uniformly distributed because of the in situ reaction and trapping effect under the rapid solidification condition. And, TiCp particles were of gradient distribution on a macro scale and their volume fraction increased from 1.86% at the layer/substrate interface to a maximum 38.4% at the surface of the layer. Furthermore, the in situ generated TiCp/gamma-Ni interfaces were free from deleterious surface reactions. Additionally, the clad coating also revealed a high microhardness of gradient variation with the layer depth and the superior abrasive wear resistance.

Influence factors on wear resistance of two alumina matrix composites

We measured the wear resistances of alumina, alumina/silicon carbide composite and alumina/mullite composite by abrasive wear. And we studied the influence of fracture mode and worn surface pullout on wear resistance. The results are as follows: the main wear mechanisms of alumina and alumina/silicon carbide were fracture wear and plastic wear respectively, and for alumina/mullite composite, fracture wear and plastic wear mechanisms worked together. The wear resistance of the alumina/silicon carbide composite and the alumina/mullite composite was better by a factor of 1 similar to 3 than that of the monolithic alumina. There were two main reasons for the better wear resistance, i.e., the improved mechanical properties and the more smooth worn surfaces. However, The primary reason was the reduction of area fraction of pullout on the worn surfaces induced by fracture mode transition. (C) 2007 Published by Elsevier B.V.

Wear resistance of reaction sintered alumina/mullite composites

Alumina and alumina/mullite composites with mullite content of 0.96-8.72 vol.% were subjected to an abrasive wear test under loads of 0.1-2.0 N with a ball-on-disc apparatus. The wear rate and area fraction of pullout f(po) on the worn surfaces were measured. The wear resistances of the alumina/mullite composites were better by a factor of 1-2 than that of pure alumina. The main wear mechanism of alumina is fracture wear, and for alumina/mullite composites, fracture wear and plastic wear mechanisms work together. The influence of mechanical properties on wear resistance was estimated by Evans' method. It was found that the wear rate depends on f(po), and the primary reason for the better wear resistance of alumina/mullite composites is the reduction off, induced by fracture mode transition. (c) 2007 Elsevier B.V. All rights reserved.

Microstructure and high-temperature wear and oxidation resistance of laser clad gamma/W2C/TiC composite coatings on gamma-TiAl intermetallic alloy

There are very strong interests in improving the high-temperature wear resistance of the y-TiAl intermetallic alloy, especially when applied as tribological moving components. In this paper, microstructure, high-temperature dry sliding wear at 600 degrees C and isothermal oxidation at 1000 degrees C on ambient air of laser clad gamma/W2C/TiC composite coatings with different constitution of Ni-Cr-W-C precursor mixed powders on TiAl alloy substrates have been investigated. The results show that microstructure of the laser fabricated composite coatings possess non-equilibrium microstructure consisting of the matrix of nickel-base solid solution gamma-NiCrAl and reinforcements of TiC, W2C and M23C6 carbides. Higher wear resistance than the original TiAl alloy is achieved in the composite coatings under high-temperature wear test conditions. However, the oxidation resistance of the laser clad gamma/W2C/TiC composite coatings is deceased. The corresponding mechanisms resulting in the above behaviors of the laser clad composite coatings are discussed. (c) 2006 Elsevier B.V. All rights reserved.

Effects of La2O3 on Microstructure and Wear Properties of Laser Clad gamma/Cr7C3/TiC Composite Coatings on TiAl Intermatallic Alloy

The effects of La2O3 addition on the microstructure and wear properties of laser clad gamma/C(r)7C(3)/TiC composite coatings on gamma-TiAl intermetallic alloy substrates with NiCr-Cr3C2 precursor mixed powders have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive spectrometer (EDS) and block-on-ring wear tests. The responding wear mechanisms are discussed in detail. The results are compared with that for composite coating without La2O3. The comparison indicates that no evident new crystallographic phases are formed except a rapidly solidified microstructure consisting of the primary hard Cr7C3 and TiC carbides and the gamma/Cr7C3 eutectics distributed in the tough gamma nickel solid solution matrix. Good finishing coatings can be achieved under a proper amount of La2O3-addition and a suitable laser processing parameters. The additions of rare-earth oxide La,03 can refine and purify the microstructure of coatings, relatively decrease the volume fraction of primary blocky Cr7C3 to Cr7C3/gamma eutectics, reduce the dilution of clad material from base alloy and increase the microhardness of the coatings. When the addition of La2O3 is approximately 4 wt.%, the laser clad composite coating possesses the highest hardness and toughness. The composite coating with 4 wt.%La2O3 addition can result the best enhancement of wear resistance of about 30%. However, too less or excessive addition amount of La2O3 have no better influence on wear resistance of the composite coating.

Wear Studies of Hydroxyapatite Composite Coating Reinforced by Carbon Nanotubes

Multi-walled carbon nanotubes (CNTs) have been successfully introduced into hydroxyapatite (HA) coatings using laser surface alloying. It is evident from transmission electron microscopy (TEM) observations that the CNTs present in the matrix still keep their multi-walled cylinder graphic structure, although they undergo the laser irradiation. Scratching test results indicated that the as-alloyed HA composite coatings exhibit improved wear resistance and lower friction coefficient with increasing the amount of CNTs in the precursor material powders. These composites have potential applications in the field of coating materials for metal implants under high-load-bearing conditions. (c) 2006 Elsevier Ltd. All rights reserved.

Influences Of Precursor Constitution And Processing Speed On Microstructure And Wear Behavior During Laser Clad Composite Coatings On Gamma-Tial Intermetallic Alloy

The effects of constitution of precursor mixed powders and scan speed on microstructure and wear properties were designed and investigated during laser clad gamma/Cr7C3/TiC composite coatings on gamma-TiAl intermetallic alloy substrates with NiCr-Cr3C2 precursor mixed powders. The results indicate that both the constitution of the precursor mixed powders and the beam scan rate have remarkable influence on microstructure and attendant hardness as well as wear resistance of the formed composite coatings. The wear mechanisms of the original TiAl alloy and laser clad composite coatings were investigated. The composite coating with an optimum compromise between constitution of NiCr-Cr3C2 precursor mixed powders as well as being processed under moderate scan speed exhibits the best wear resistance under dry sliding wear test conditions. (C) 2008 Elsevier Ltd. All rights reserved.

Influence of processing medium on frictional wear properties of ball bearing steel prepared by laser surface melting coupled with bionic principles

Coupling with bionic principles, an attempt to improve the wear resistance of ball bearing steel (GCr15) with biomimetic units on the surface was made using a pulsed Nd: YAG laser. Air and water film was employed as processing medium, respectively. The microstructures of biomimeitc units were examined by scanning electron microscope and X-ray diffraction was used to describe the microstructure and identify the phases as functions of different mediums as well as water film with different thicknesses. The results indicated that the microstructure zones in the biomimetic specimens processed with water film were more refined and had better wear resistance increased by 55.8% in comparison with that processed in air; a significant improvement in microhardness was achieved by laser surface melting. The application of water film provided considerable microstructural changes and much more regular grain shape in biomimetic units, which played a key role in improving the wear resistance of ball bearing steel. (c) 2010 Elsevier B.V. All rights reserved.

Formation and structure of composite coating of HDA and micro-plasma oxidation on A3 steel

Composite coatings were obtained on A3 steel by hot dipping aluminum(HDA) at 720 ℃ for 6 min and micro-plasma oxidation(MPO) in alkali electrolyte. The surface morphology, element distribution and interface structure of composite coatings were studied by means of XRD, SEM and EDS. The results show that the composite coatings obtained through HDA/MPO on A3 steel consist of four layers. From the surface to the substrate, the layer is loose Al2O3 ceramic, compact Al2O3 ceramic, Al and FeAl intermetallic compound layer in turn. The adhesions among all the layers are strengthened because the ceramic layer formed at the Al surface originally, FeAl intermetallic compound layer and substrate are combined in metallurgical form through mutual diffusion during HDA process.Initial experiment results disclose that the anti-corrosion performance and wear resistance of composite coating are obviously improved through HDA/MPO treatment.

Microstructural features of an iron-based laser coating

A high toughness wear resistant coating is produced by laser clad Fe-Cr-W-Ni-C alloys. The microstructural and compositional features of the laser-solidified microstructures and phase evolutions occurring during high temperature tempering at 963 K were investigated by using analytical electron microscopy with energy dispersive X-ray analysis. The clad coating possesses the hypereutectic microstructure consisted of M7C3 + (Y + M7C3) Du ring high temperature aging, the precipitation of M23C6 and M2C in austenite and in situ transformation of dendritic M7C3 to M23C6 and eutectic M7C3 to M6C occurred. The laser clad coating reveals an evident secondary hardening and superior impact wear resistance.

Micro/Nanomechanical and Tribological Properties of thin Diamond-Like Carbon Coatings

The diamond-like carbon (DLC) films with different thicknesses on 9Crl8 bearing steels were prepared using vacuum magnetic-filtering arc plasma deposition. Vickers indentation. nanoin-dentation and nanoscratch tests were used to characterize the DLC films with a wide range of applied loads. Mechanical and tribological behaviors of these submicron films were investigated and interpreted. The hardnesses of 9Crl8 and DLC, determined by nanoindentation, are approximately 8GPa and 60GPa respectively; their elastic moduli are approximately 25OGPa and 600GPa respectively. The friction coefficients of 9Crl8, DLC. organic coating, determined by nanoscratch, are approximately 0. 35, 0. 20 and 0. 13 respectively. It is demonstrated that nanoindentation and nanoscratch tests can provide more information about the near-surface elastic-plastic deformation, friction and wear properties. The correlation of mechanical properties and scratch resistance of DLC films on 9Crl8 steels can provide an assessment for the load-carrying capacity and wear resistance

Microstructure and Tribological Properties of Laser Clad gamma/Cr7C3/Tic Composite Coatings on gamma-TiA1 Intermetallic Alloy

In order to improve the wear resistance of the gamma-TiAl intermetallic alloy, microstructure, room- and high-temperature (600 degrees C) wear behaviors of laser clad gamma/Cr7C3/TiC composite coatings with different constitution of NiCr-Cr3C2 precursor-mixed powders have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive spectrometer (EDS), block-on-ring (room-temperature) and pin-on-disk (high-temperature) wear tests. The responding wear mechanisms are discussed in detail. Results show that microstructures of the laser clad composite coatings have non-equilibrium solidified microstructures consisting of primary hard Cr7C3 and TiC carbides and the inter-primary gamma/Cr7C3 eutectic matrix, about three to five times higher average microhardness compared with the TiAl alloy substrate. Higher wear resistance than the original TiAl alloy is achieved in the clad composite coatings under dry sliding wear conditions, which is closely related to the formation of non-equilibrium solidified reinforced Cr7C3 and TiC carbides and the positive contribution of the relatively ductile and tough gamma/Cr7C3 eutectics matrix and their stability under high-temperature exposure.

Substrate Effects on the Micro/Nanomechanical Properties of TiN Coatings

Nanoindentation and nanoscratch tests were performed for titanium nitride (TiN) coatings on different tool steel substrates to investigate the indentation/scratch induced deformation behavior of the coatings and the adhesion of the coating–substrate interfaces and their tribological property. In this work, TiN coatings with a thickness of about 500 nm were grown on GT35, 9Cr18 and 40CrNiMo steels using vacuum magnetic-filtering arc plasma deposition. In the nanoindentation tests, the hardness and modulus curves for TiN/GT35 reduced the slowest around the film thickness 500 nm with the increase of indentation depth, followed by TiN/9Cr18 and TiN/40CrNiMo. Improving adhesion properties of coating and substrate can decrease the differences of internal stress field. The scratch tests showed that the scratch response was controlled by plastic deformation in the substrate. The substrate plays an important role in determining the mechanical properties and wear resistance of such coatings. TiN/GT35 exhibited the best load-carrying capacity and scratch/wear resistance. As a consequence, GT35 is the best substrate for TiN coatings of the substrate materials tested.

Microstructure and mechanical properties at TiCp/Ni-alloy interfaces in laser-synthesized coatings

Titanium carbide particle (TiCp) reinforced Ni alloy composite coatings were synthesized by laser cladding using a cw 3 kW CO2 laser. Two kinds of coatings were present in terms of TiCp origins, i.e. undissolved and in situ reacted TiCp, respectively. The former came from the TiCp pre-coated on the sample, whereas the latter from in situ reaction between titanium and graphite in the molten pool during laser irradiation. Conventional and high-resolution transmission electron microscope observations showed the epitaxial growth of TiC, the precipitation of CrB, and the chemical reaction between Ti and B elements around phase interfaces of undissolved TiCp. The hardness, H, and elastic modulus, E, were measured by nanoindentation of the matrix near the TiCp interface. For undissolved TiCp, the loading curve revealed pop-in phenomena caused by the plastic deformation of the crack formation or debounding of TiCp from the matrix. As for in situ generated TiCp, no pop-in mark appears. On the other hand, in situ reacted TiCp led to much higher hardness and modulus than that in the case of undissolved TiCp. The coating reinforced by in situ generated TiCp displayed the highest impact wear resistance at both low and high impact conditions, as compared with coatings with undissolved TiCp and without TiCp. The impact wear resistance of the coating reinforced by undissolved TiCp increases at a low impact work but decreases at a high impact work, as compared with the single Ni alloy coating. The degree of wear for the composite coating depends primarily on the debonding removal of TiCp.

Nonequilibrium microstructures and phase evolutions of an iron-based laser clad coating

The microstructural and compositional features of the laser-solidified microstructures and phase evolutions occurring during high temperature tempering were investigated by using analytical electron microscopy with energy dispersive X-ray analysis. The cladded alloy, a powder mixture of Fe, Cr, W, Ni and C with a weight ratio of 10:5:1:1:1, was processed with a 3 kW continuous wave CO2 laser. The cladded coating possessed the hypoeutectic microstructure of the primary dendritic gamma-austenite and interdendritic eutectic consisting of (gamma+M7C3). The gamma-austenite is a nonequilibrium phase with extended solid solution of alloying elements. And, a great deal of fine structures, i.e., a high density of dislocations, twins, and stacking faults existed in austenite phase. During high temperature aging, the precipitation of M23C6, MC and M2C in austenite and in situ transformation of M7C3(+gamma) --> M23C6 and M7C3+gamma --> M6C occurred. The laser clad coating revealed an evident secondary hardening and superior impact wear resistance.