José M. Castanho

Study of tungsten sputtered films with low nitrogen content

Abstract In this work, tungsten coatings doped with small percentages of nitrogen (% N at %) were deposited by sputtering and their characterization was focused in view of a possible future application as hard coatings. The films show an α-W (bcc) structure, significant changes in the X-ray diffraction peak positions not having been observed for the films containing nitrogen; however, these films have broader peaks than pure W films. All the films present a very dense cross-section morphology. Higher hardness values were found for the tungsten films containing nitrogen ( HV = 15 GPa → HV = [40–50 GPa ]). The scratch-test results show that the coatings fail cohesively, firstly by tensile cracking for loads in the range [30–40 N] and after by chipping for loads in the range [50–60 N]. Pure W films present only tensile cracking. The films are structurally stable up to 700°C annealing temperatures, even for a 12 h annealing time, only a narrowing of the diffraction peaks in relation to the as-deposited state being obtained. The hardness does not suffer significant alterations with increasing temperatures and annealing times.

Fine tuning injection feedstock by nano coating SS powder

The carbon-enriched atmospheres commonly experienced during debinding can lead to abnormal grain growth and chromium depletion in stainless steels. Coating powder particles with nano-structured layers can block the phenomenon, Portuguese researchers have found…

Effect of the Ni chemical distribution on the reactivity and densification of WC-(Fe/Ni/Cr) composite powders

The objective of this work was to study the effect of the Ni distribution on the reactivity and densification of WC-(Fe/Ni/Cr) composite powders. For such, stainless steel AISI 304, was used as a binder base composition which was enriched with Ni by three different processing methods: WC sputter deposition using a target of stainless steel with Ni discs, conventional wet milling of commercial powders (WC, stainless steel and Ni powders) and a previous coating of the WC particles with Ni, followed by the conventional mixing of this coated powder with stainless steel powder. The reactive sintering of these composite powders with identical compositions was investigated. The powder compacts were characterized by scanning electron microscopy and X-ray diffraction with Rietveld analysis to quantify de crystalline phases present.

The influence of nitrogen on the mechanical behaviour of multilayered coatings

Abstract Multilayered films are a new kind of coating that belong to a more plentiful family of materials labelled as nanostructured materials. These kinds of coatings stand in the frontier of investigation in thin films for structural applications. In the present work, multilayered coatings with alternated layers of WTi(N) and Ag were deposited to be used as wear resistant surfaces. The association of the high hardness, wear resistance of WTi(N) layers [Proceedings of the Eleventh LAWPSP Symposium, SL1.1-SL1.7, Bombay, India (1998); Surf. Coat. Technol., 102 (1998), 50] and the good ductility of the silver ones is the guarantee of obtaining a better mechanical performant coating. However, to reach a satisfactory comprehension of the behaviour of the coatings in service a true understanding of some important properties is needed. For this reason, hardness, Young modulus, internal stresses and adhesion were evaluated, as well as function of the number and thickness of the layers.

Improving the Cutting Performance of TiAlN Coatings Using Submicron Metal Interlayers

TiAlN coatings as been used with success in high speed metal machining. The similar B1 TiN structure, high hardness, adhesion and high wear and oxidation resistance contributes to such ability. However, it is possible to enhance some of those properties, particularly the adhesion and cohesion of the coatings without changing significantly all the others. The introduction of submicron metal interlayers in TiAlN coatings do not affect significantly the hardness of the whole coating itself, but promote a beneficial decrease in the internal stresses and an increase in the film adhesion and cohesion which contributes to improve their performance in service. Moreover, the possibility to form morphological discontinuities in the coating due to the presence of metal interlayers can enhance diffusion barriers. So, in the present work, multilayer coatings of TiAlN with Al and Ti interlayers with approximately 3.5μm thick were sputtered. The internal stress, hardness, Young modulus and adhesion of the coatings were evaluated as a function of number of layers.

Microwaves show off their advantages in efficient sintering

Recent research on the ability of powdered metals to absorb and dissipate microwave radiation opened new opportunities for powder metallurgy. Microwave sintering can be an efficient, economic and valuable approach for the processing of some PM materials. There are some other advantages too…

Reinforcement Coating on Stainless Steel and Copper Powders

The continuous miniaturization of the mechanical components and devices push to microfabrication techniques such as μPIM (micro-Powder Injection Moulding) and laser sintering, particularly DMLS (Direct Metal Laser Sintering) [1]. To achieve such proposes novel feedstocks involving metal powders with enhanced surfaces properties are required. The conventional powders production, gas and water atomization does not fulfil these surface properties. In order to produce particles with a higher surface-to-volume ratio, the surface morphology of the particles must be modified. The powders’ surface can be tailored by the presence of a thin film. Moreover, magnetic and sintering properties can be adapted with convenient thin films of different metals. Micrometric commercial copper (99% purity) and austenitic stainless steel 316L powders with two different shapes: irregular and spherical were used as the starting material. These powders were coated in a modified home sputtering device. Stainless steel (SS) 304L and copper nanostructured thin films were deposited on copper and on SS 316L powders, respectively. The coating procedure were tailored to enhance the magnetic properties of the copper powders [2], and to extend the liquid phase sintering, improving the performance of the sintered parts of SS 316L powders [3]. The coated and uncoated powders have been subjected to microstructural studies by environmental scanning electron microscope (SEM) coupled with energy dispersive spectroscopy (EDS) and backscattered electron (BSE) and for the coated ones were made Electron Probe Micro Analysis (EPMA). The deposition method is able to coat homogeneously the powders’ surface, as can be observed by the SEM image with a backscattered electron (BSE) detector (figure 1).

Chapter 16 – Hard Coatings Based on Metal Nitrides, Metal Carbides and Nanocomposite Materials: PVD Process and Properties

In the last 30 years the hard coatings deposition technology was strongly improved. Besides the traditional surface treatments, new deposition technologies emerged and were implemented industrially. Such surface technologies answered the increasing demands imposed by the automation of the processes and the requirements of more performing materials to be used in aggressive environments. Deposition temperature, thickness of coatings, working temperature, and atmosphere, mechanical solicitations, cutting speeds, workpiece material and lubrication are the parameters that should be considered in the selection of the surface modification technology. Among the available surface modification technologies, the physical vapor deposition (PVD) has been elected as the most reliable, environmental friendly and the one with the best performance for depositions of new materials, which cannot be produced using conventional surface-deposition technologies. The properties of thin films, such as the hardness of structural and protective coatings, depend on the grain size, morphology, density and internal stress and this dependence makes it important to understand processing-microstructure-property relationships. Considering the hard coatings, the main requirements for advanced ones are the following: ⊙ The optimum surface quality, in order to improve the tribologic behavior, decreasing the need of coolants and lubricants.

Laminated Composite Thin Films: A Solution to Improve Cutting Tools Performance

In cutting applications hard thin films of coated tools are expected to be wear and oxidation resistants, and with strong adhesion to the substrate. Due to the high loads involved in the contacts, the main efforts must be supported by the substrate and it is supposed that the coatings follow their elasto-plastic deformation, with a subsequent delay of the crack propagation. The commercial thin films used for these applications are generally monolithic and homogeneous or heterogenous(chemical compositional gradient up-down). Even the nanostructured coatings will perform under these loads as monolithic coatings, and the crack generation and propagation will be ruled by the same mechanisms as in the monolithic coatings. Hence, the hard coatings for cutting tools must be able to deflect surface cracks and exhibit the highest adhesion to the substrate. In order to achieve these characterisitics, the common Ti-Al-N was selected as hard coating, and thin ductile metal interlayers (few tenths of nanometres) were introduced inside Ti-Al-N thin film as long period multilayer coatings – nanolaminate coatings. The presence of interlayers revealed efficiency in dissipation of the energy generated during the application, decreasing the propagation cracks across the coating and ensuring the best adhesion. The mechanical behavior observed is homotethic of macrolaminate composite bulk materials. The failure of the coating is layer-by-layer, always exposing the ductile layer, which function is also to be a fuse that protect the remaining coating. The material of the interlayer and the period (interlayer/coating) selected resulted from the balance between the maximum performance of coating to avoid service failure and the minimum decrease of relevant mechanical properties of the monolitic hard coating as hardness.