Surface Engineering Processes Research Articles

Contact mechanics modelling of surface engineered systems

The ever-increasing demands for combined properties in modern machinery operating under ever more severe conditions have been the driver for the rapid developments of many advances surface engineering technologies. Designers thus have many surface engineering technologies to select from in the design of components. However, it also presents challenges to designers to select an optimal surface engineering process for a specific application. To this end, a contact mechanics model has been developed based on modern theories of multilayered surface contact, taking into account the multilayered structure, real surface roughness and friction effects. With this model, the performance of surface engineered components can be successfully predicted. In this paper, the development of Hertz contact theory is first reviewed, the Birmingham multilayered real rough surface contact mechanical model is discussed and a number of major steps towards designing dynamically loaded surface engineered components are demonstrated by case studies.

Allan variance of frequency fluctuations due to momentum exchange and thermomechanical noises

We investigate the Allan variance of nanoresonators with random rough surfaces under the simultaneous influence of thermomechanical and momentum exchange noises. Random roughness is observed in various surface engineering processes, and it is characterized by the roughness amplitude w, the lateral correlation length ξ, and the roughness exponent 0<H<1. The roughness influence becomes significant for measurement time τA so that ωoτA∼1, with ωo the fundamental resonance frequency. The Allan variance increases significantly with increasing roughness (decreasing H and/or increasing ratio w∕ξ) if the quality factor due to gas collisions is smaller than the intrinsic quality factor associated with thermomechanical noise.

Investigation into LST and its Novel Application in Mould

Laser surface texturing (LST) technology that is firstly used in rollers, is a specialized surface engineering process capable of enhancing the surface material properties, wear resistance, fretting fatigue life and reducing friction. This practical technology of the LST process is based on a pulsating laser beam that, by material ablation, generates the optimum topographical surface. In order to exploit the full potential of the process, a great amount of research has explored from the material removal mechanics to the development of the LST process. This paper reports on the LST research involving the LST technology surveying process optimization, LST equipment and its industrial applications. The paper also highlights the forming theory describing the skin-pass process of transferring the textured roller’s surface structure onto the steel sheet, and the laser-matter interaction that occurs when and intense laser beam is tightly focused in the workpiece surface. It presents the influence of various factors affecting the textured workpiece performance together with the investigations into tribology of textured components. The paper also discusses these developments and some fundamental on future LST research.

Tribological characteristics of ceramic conversion treated NiTi shape memory alloy

NiTi shape memory alloys are very attractive for medical implants and devices (such as orthopaedic and orthodontic implants) and various actuators. However, wear is a major concern for such applications and a novel surface engineering process, ceramic conversion treatment, has recently been developed to address this problem. In this study, the tribological characteristics of ceramic conversion treated NiTi alloy have been systematically investigated under dry unidirectional wear, reciprocating-corrosion wear and fretting-corrosion wear condition. Based on the experimental results, the wear behaviour under different conditions is compared and wear mechanisms involved are discussed.

Surface Engineering for Adhesively Bonded Metal-Composite Joints

Recently, many nations along with private shipbuilders have begun developing large maritime vessels using composite materials structurally. Concurrently, the US Navy has a need for research on bonded metal-composite joints. For these reasons, a literature review was conducted to establish a fundamental knowledge base of adhesive bonding and failure theories along with surface cleaning and engineering processes that would be valuable for metal-composite joint designs. It is believed that by understanding bonding and failure fundamentals, optimal surface characteristics can be targeted. Furthermore, by knowing the available cleaning and surface engineering processes, in conjunction with understanding their resulting surface topographies and compositions, creative and novel joints can be designed. This report provides the results of the literature review performed, which serves as a platform for future research aimed at optimizing bonded joints for use in naval applications.

Accelerated formation of multicellular 3‐D structures by cell‐to‐cell cross‐linking

The three-dimensional (3-D) arrangement of cells within tissues is integral to their development and function. Advances in stem cell science and regenerative medicine have stimulated interest in the replication of this architecture in vitro. We have developed a versatile method for controlling short-term cell-cell and cell-matrix interactions via a facile cell surface engineering process that enables the rapid formation of specific 3-D interactions for a range of cell types. We demonstrate that chemical modification of cell surfaces and matrix proteins can artificially accelerate the cell adhesion process and confirm the ability to control the formation of multicellular aggregates with defined architectures and heterotypic cell types. Direct comparison with a natural aggregation process seen during differentiation of embryonic stem (ES) cells revealed increased expression of developmental regulatory proteins and a concomitant enhancement of ES cell differentiation. Furthermore, this new methodology has numerous applications in generating layered structures. For example, we demonstrate improved transfer of therapeutic human keratinocytes onto a dermal layer in a skin repair model.

Plasma-based physical vapor deposition surface engineering processes

Plasma-based physical vapor deposition (PVD) process developments occurring over the past few decades now allow the production of tribological coatings with properties which were previously unachievable. These new coatings will be critical in the creation of new products with improved functionality and performance, which will have a dramatic impact on, for example, their operating efficiency and lifetime. The key pioneers behind these PVD developments are discussed here, together with some significant process innovations. The latter include ionization-enhancing systems, such as thermionic assistance and arc evaporation, as well as unbalanced magnetron sputtering and magnetic plasma confinement. These developments have provided the impetus behind the recent growth in the technology field which we now know as surface engineering, and the recognition that surfaces provide the functionality and durability for almost all engineered products. Vacuum plasma technologies can thus be regarded as critical, not only for functional devices and thin film applications (for which their importance was previously most recognized), but also for structural product applications; they will thus underpin the entire spectrum of manufacturing industry.

Heat treatment and surface engineering in the production of automotive components

Origin The conference was the outcome of a discussion held in Beijing in 1997 which considered the value of international collaboration with Thailand. The participants in that discussion were Professor Tom Bell, Robert Wood (as members of IFHTSE Executive Committee), and Dr John Pearce (MTEC and Chiang Mai University). The 1997 economic downturn in Asia ± Paci® c put planning on hold, but the idea was revived, and early in 2002 meetings were held between IFHTSE and MTEC contacts. The outcome was a plan for a small conference on an automotive theme, in or around Bangkok. A planning team, along with the IFHTSE Executive Committee, noted that investment by most of the major global carmakers had been attracted to Thailand early in the 1990s. The perception of the country and its engineering potential was very positive. It was also seen to offer political and social stability and there was a willingness to ease some of the usual dif® culties for investors. By 2001/2 Thailand showed signs of having pulled out of the trough rather better than some other countries in the region. Manufacturing companies are taking a more positive view of the stable position of Thailand, with China and India also giving considerable priority to automotive production. It is likely, therefore, that the Asia ± Paci® c region will see some interesting developments in supply and demand in the automotive industry. Thailand restarts from a promising baseline, and the big names are still there. There will, however, be no advantage in producing `old tech’ vehicles. Production will have to be state of the art with all the new global pressures for weight reduction, ef® ciency, and emissions reduction. Heat treatment and surface engineering processes play a crucial role in the successful production of reliable, wear resistant and recyclable automotive components. Success in this ® eld is not con® ned to the OEMs; increasingly, the whole supply chain is involved in process development and quality assurance. The gradual global adoption of TS 16949:2002 will change the way in which the suppliers relate to the vehicle manufacturer. In Thailand, the downturn arrested the development of a tier 1 and tier 2 automotive supplier structure. The remaining suppliers in Thailand tend to be Japanese or US owned, but a much more diverse and elaborate structure of suppliers and subcontractors will be needed to support growth. This offers considerable opportunities for SMEs as well as larger companies. A further implication is a demand for a domestic supply of competent engineers. The signs suggest that Thailand can satisfy that need very well. There are said to be around 100 engineering schools/departments in the country, turning out about 10 000 graduates annually across the engineering disciplines. One problem is that many of these engineers have been educated almost entirely in Thai; the authorities are now emphasising the need to distribute more English language education and training materials and to increase the capabilities of Thai engineers in the use of English and other world languages. It was therefore concluded that a degree of urgency was needed in scheduling the conference. The organisational and administrative time available was short, but enthusiasm was generated and the competence of the MTEC staff overcame the dif® culties involved.

Cleanliness Standards and Defining Acceptable Cleanliness Levels: Analytical Techniques, Particulate Monitoring, and Successful Analytical Testing

A clean surface can be critical in surface engineering processes. Particles on the surface may interfere with the surface modification process causing defects and poor performance. Therefore, the level of cleanliness required in a particular application is defined by the final product performance and appearance. This paper describes a number of analytical techniques that are used to assess the cleanliness of a surface. Practical examples are also given of how these techniques have been used in industry to investigate problems associated with maintaining cleanliness levels and to identify sources of contamination.

Effects of rare earth additions on nitriding of EN40B by plasma immersion ion implantation

Reports over the last two decades have shown the potential for improving existing thermochemical surface engineering processes by rare earth (RE) additions. Some theories for the mechanism by which RE additions have an effect suggest that they can act as catalysts for the reactions that take place in the treatment atmosphere. In plasma nitriding, this is reported to provide an increased supply of nitrogen to the component surface. Thus, there is better nitrogen uptake by the component material. Therefore, treated component properties can be improved, attributed to enhanced diffusion of nitrogen. Here, the effects of small lanthanum RE additions to PI 3 treatment of steels are discussed. It is shown that RE addition in the form of a small solid piece in the centre of the negatively biased work table results in increased nitrogen concentrations in the near surface regions of steel specimens coupled with improved surface hardness properties. The same small piece of RE can be reused for several consecutive PI 3 treatments, making this potentially a cost-effective method for improving the treatment of steels by PI 3.

Shot peening of plasma nitrided steel for fretting fatigue strength enhancement

The potential of fretting fatigue strength enhancement by a duplex surface engineering process involving shot peening of plasma nitrided steel, termed duplex SP/PN, is demonstrated. Specimens of 709M40 steel were individually plasma nitrided, shot peened, or duplex SP/PN treated. Fretting fatigue properties of the surface engineered specimens were evaluated. Surface roughness, residual stress, and hardening effect following the various surface treatments were examined and compared. It has been found that the duplex treatment can significantly improve the fretting fatigue strength of the investigated low alloy steel. Under the present testing conditions, the duplex SP/PN treatment increased the fretting fatigue strength (at 107 cycles) of 709M40 steel by more than 70% relative to the nitrided, 120% to the shot peened, and 500% to the untreated steel. The improvement has been explained in terms of the significantly increased surface hardness and compressive residual stress in the near surface region following the duplex SP/PN treatment. By analysing the stress distributions in a shot peened surface, the influence of surface roughness on fretting fatigue strength is also discussed.

Dry sliding wear behaviour at ambient and elevated temperatures of plasma transferred arc deposited aluminium composite coatings

Plasma transferred arc (PTA) surfacing is a surface engineering process in which a coating is deposited on the substrate by the injection of metal powders and/or ceramic particles into the weld pool created by the formation of a plasma plume. The present work involved the tribological evaluation of metal matrix composite (MMC) coatings deposited onto an aluminium alloy using the PTA technique. Coatings were fabricated by the deposition of an Al–Ni powder containing either Al2O3 or SiC particles. Dry sliding wear behaviour of the coatings was evaluated at ambient and elevated temperatures. Under sliding conditions of low applied stress and ambient temperature, reinforcement properties such as interfacial structure and fracture toughness have a significant influence on wear resistance. The SiC particles, which exhibit high interfacial bonding and toughness, support the matrix by acting as load bearing elements, thereby delaying the transition in wear mechanism as applied stress increases. As applied stresses exceed the fracture strength of the SiC and Al2O3 particles, these particles suffer fragmentation and/or debonding and no longer support the matrix. At higher stresses and elevated temperature, matrix properties such as flow stress and the tribolayer formation play more important roles in determining wear resistance.

Mechanical properties of laser-deposited composite boride coating using nanoindentation

Nanoindentation proves to be an effective technique to measure mechanical properties of “composite” materials, as it has high spatial resolution that enables estimation of properties even from fine grains, particles, and precipitates. The elastic modulus, E, of the composite boride coating deposited on AISI 1010 steel using the laser surface engineering (LSE) process has been computed using the nanoindentation technique. The highest E value of 477.3 GPa was achieved for coating in a sample that contained 0.69 volume fraction of TiB2 particles in the coating after processing with the highest laser traverse speed of 33 mm/s. A comparison between the theoretical and experimental computation of the elastic modulus suggests that theoretical elastic modulus values are lower than computed elastic modulus, as the latter includes the effect of dissolution of fine TiB2 particles in Fe matrix and metastable phase formation such as Fe a B b and Ti m B n . Dissolution of fine TiB2 particles in the Fe matrix in the coating region has been corroborated by transmission electron microscope (TEM) micrographs and corresponding energy-dispersive spectroscope (EDS) analysis and selected area diffraction (SAD) pattern.

Properties of the surface layers on titanium alloy and their biocompatibility in in vitro tests

Recently, it has been suggested that the future designs of implants and endoprothesis should be focused on the use of a new generation of biocompatible, corrosion and wear resistant materials or materials currently used but modified by surface engineering processes. The aim of the study was to investigate the features of titanium oxide and titanium nitride layers produced on titanium alloy by plasma nitriding and oxidizing under glow discharge conditions and their biocompatibility in in vitro tests. The plasma nitriding and oxidizing techniques essentially improved the properties of titanium alloys. Their microstructure and the results of hardness, wear and corrosion resistance tests are presented. In the investigations of the cellular responses of human fibroblast cells to these layers, three aspects were considered: the number of growing cells, their morphological features and their biological corrosion resistance. Nitriding and oxidizing under glow discharge conditions have provided new possibilities of producing non-toxic, human fibroblast-compatible surface layers on parts made of titanium alloys with sophisticated shapes. Uniform surface layers having a controlled microstructure and phase composition can contribute to the opening of a wider application range of titanium alloys as biomaterials.

Low temperature plasma carburising of austenitic stainless steels for improved wear and corrosion resistance

A novel plasma surface engineering process has been developed for engineering the surfaces of austenitic stainless steels to achieve combined improvements in wear and corrosion resistance. The process employs carbon as the major alloying species in the glow discharge of a plasma, facilitating the diffusion of carbon into the surfaces of various austenitic stainless steels and forming a precipitate free layer supersaturated with carbon at relatively low temperatures. This low temperature plasma surface alloying process produces a surface engineered layer several tens of micrometres thick, which has a high hardness together with excellent wear and corrosion resistance. The present paper describes various aspects of the novel process, concerning processing, structures, properties, and applications to engineering components.

Surface engineering of titanium alloys for wear protection

This paper describes the reasons for the generally poor tribological behaviour of titanium alloys. It describes surface engineering processes currently used in the protection of titanium alloy surfaces against wear including plasma spraying, physically vapour-deposited coatings, electrolytic and electroless plating, ion implantation and anodizing. The advantages and disadvantages of the various processes are indicated and typical components treated by these processes are described. Thermochemical processes and energy beam alloying surface engineering processes applied to titanium alloys are described in greater detail. Contemporary research and development in these areas are described, particularly where the objective is the production of surface hardening to depths comparable with those used in conventional transmission materials such as in nitrided steels.

Ceramic/Metal Interface in Laser Deposited Hard Refractory Composite Coating: Electron Microscopic Study / Keramik/Metall-Grenzfläche einer durch Laserabscheidung erzeugten Beschichtung an harten hochschmelzenden Verbunden: Elektronenmikroskopische Untersuchungen

Ceramic-metal interface plays the prime role in estimation of properties of composite and similar materials. In the present study, TiB 2 has been deposited on AlSI 1010 steel using laser surface engineering (LSE) process. TiB 2 /Fe interface is examined by electron microscopy (SEM and TEM) at microstructural and atomic level. A continuous, crack free and metallurgically bonded coating is obtained which is composite in nature. TiB 2 particles are randomly distributed in Fe matrix without any preferred crystallographic orientation. High resolution transmission electron microscopy (HRTEM) shows that TiB 2 /Fe interface is atomically smooth and sharp with very little mismatch. There is no evidence of cracking or delamination at the interface. However, a small reaction zone of approximately 100 nm is formed at the interface as a consequence of non-equilibrium synthesis during LSE process.

Engineering surfaces—a philosophy of manufacture (a proposal for good manufacturing practice)

This paper considers a new approach to controlling the finishing process of engineering surfaces to ensure that their final topography and surface mechanical properties make them suitable for the intended functional purpose. It is proposed that this ‘engineering’ of the final surface is achieved by controlling the final machining or surface working process to impart the required mechanical properties. It is shown in the paper that some surface engineering processes are already employed by industry but that many of these processes are implemented through an empirical understanding of them. The intention of the paper is to lay down a basis for a more rigorous approach to engineering surfaces for their final function.

Plasma-based surface engineering processes for wear and corrosion protection

Vacuum plasma-based coating and treatment methods have considerable potential for reducing wear and corrosion. However, they have not been widely applied to engineering components other than tools such as those used in metal cutting. This is due to several factors, not least of which are cost and an unsuitability for cheaper substrate materials. Here we discuss six plasma-based processing routes that can widen the applicability of these processes and ensure greater market penetration. These methods are: (i) duplex plasma nitriding plus physical vapor deposition (PVD) coating, (ii) low temperature plasma diffusion treatment, (iii) postcoat plasma nitriding, (iv) layered diamondlike carbon/metal carbide PVD/chemical vapor deposition coating, (v) thick metal/metal nitride PVD coating, and (vi) duplex electroless nickel plus PVD coating. The characteristics of these methods are discussed, especially with regard to their beneficial influence on wear or corrosion.

Deposition of boron-nitride films by nitrogen sputtering from a boron-metal target

This contribution deals with reactive growth of boron-nitride films by a rf nitrogen-sputtering process from a boron-metal target; thus nitrogen is functioning both as sputter and reactive gas. Only few and superficial reports of reactive sputter depositions from a metallic boron target in various argon/nitrogen mixtures exist, compared to the number of reports on rf sputtering from a BN target. Nitrogen sputtering of boron-metal has previously not been reported. It was shown by Fourier-transform infrared (FTIR) spectroscopy that the hexagonal structure of BN exclusively was deposited. Sputter rates were measured and showed no dependence on the reactive-gas flow and only a marginal dependence on sputter-gas mixtures containing 20% of krypton, argon, or helium. The reported nitrogen-sputtering process appears to be appropriate for exploration of the key parameters for phase control in BN growth and for additional surface engineering processes such as substrate bias and post-ion bombardment.