Surface Engineering Techniques and Applications

Magnesium and its alloys are a well-explored type of material with a multitude of applications ranging from biomedical prosthetics to non-biological tools such as automotive components. The use of magnesium and its alloys are highly desired for such applications mainly because magnesium is lightweight and possesses a high strength to weight ratio, which reduces the amount of energy required for the operation of an apparatus. In particular, the biomedical industry uses magnesium as orthopedic implants because of its strength properties that are similar to organic bone structures. Additionally, the highly corrosive or degrading nature of magnesium makes it suitable for degradable implants or medical devices. Cast magnesium alloys are also used as components in modern engines and automobiles, as magnesium's lightweight and high strength properties permit for faster automotive speeds, acceleration, and reduced energy consumption. Magnesium produces a quasi-passive hydroxide film that offers little to no inhibition of corrosion processes. Although the degree of film passivity can be increased through metallurgical techniques like alloying, the highly oxidizing nature of magnesium remains the single most important challenge to its widespread use. This chapter provides a detailed explanation of the most successful mechanisms used to control the corrosion of magnesium and its alloys and highlights the benefits and challenges for using them.

Application of Laser Assisted Cold Spraying Process for Materials Deposition

The Laser-Assisted Cold Spraying (LACS) process is a hybrid technique that uses laser and cold spray mechanism to deposit solid powders on metal substrates. For bonding to occur, the particle velocities must be supersonic. The supersonic effects can be achieved by passing a highly compressed Nitrogen gas (˜30 bars) through de Laval supersonic nozzle. LACS is a surface coating technique that is desirable in rapid prototyping and manufacturing, particularly for biomedical applications. Current world research reveals that the capability of the LACS regarding the enhancement of surface properties of coating titanium alloys with hydroxyapatite will be essential for fabricating scaffolds for bone implants using Laser Engineered Net Shaping (LENS) technique. In this chapter, coatings of composite powders made of titanium and hydroxyapatite deposited on Ti-6Al-4V substrate by LACS technology are presented. These coatings were successfully characterised by means of X-Ray Diffraction (XRD) and optical microscopy for their phases, composition, and microstructure, respectively. The results of the produced LACS coatings compare well with those obtained with traditional thermal spray and cold spray techniques, respectively. In addition, the XRD results were found to be similar to the precursor powders, which indicated that no phase transformation occurred to HAP. Coatings comprising of other crystalline phases of HAP are less bio-integrable and fail quicker within the human body fluids environments.

Improving Surface Integrity Using Laser Metal Deposition Process

Laser Metal Deposition (LMD), an additive manufacturing process (also known as 3-D printing) and a non-traditional fabrication process used for improving the surface integrity of components is presented in this chapter. In LMD, parts are manufactured directly from the 3-D Computer-Aided Design (CAD) model data. Complex parts can be produced in a single step, which is impossible with the traditional manufacturing methods such as casting, cutting, and turning operations. The major steps required in the production of parts using the laser metal deposition process are highlighted. The flexibility offered by the LMD technique makes it an important surface engineering technique. Composite parts or parts whose surfaces are made of composite materials can also be produced in a single step because two or more dissimilar materials can be handled simultaneously in the LMD process to produce parts. This is because the building of parts in LMD is achieved by the LMD machine following the detail described by the CAD model of the part being made. The processing parameters affecting the properties of laser metal deposited parts are described in detail. This chapter establishes the ability of the LMD in the production of complex and one of its kind parts, its ability to improve surface properties, repair high-valued parts, and reduce the buy-to-fly ratio in the production of aerospace parts. It also highlights the use of non-traditional finishing techniques on laser deposited parts to further improve the surface integrity of components. The chapter is concluded by presenting a laser metal deposited Ti6Al4V/TiC composite. The laser metal deposited Ti6Al4V/TiC composite was characterized through the microstructure, microhardness, and wear resistance, and it was found that the resulting deposits were fully dense and of improved surface properties when compared to the parent materials.

Surface Engineering by Friction Stir Processing and Friction Surfacing

This chapter is focused on the recent advances in the solid state surface engineering techniques including Friction Stir Processing (FSP) and Friction Surfacing (FS). The effectiveness of FSP and FS in improving the surface properties is explained in detail along with the principles, applications, advantages, and disadvantages of these techniques. The parameters affecting FSP and FS are presented. Various surface properties improved in different alloys by FSP and FS along with the results of the recent research work is presented in this chapter. The shortcomings of the processes and ways to overcome them are discussed. The effect of FSP on pitting corrosion of AA 6082 is studied and the results are presented.

Surface Characterization in Fused Deposition Modeling

Fused deposition modeling is a proven technology, widely diffused in industry, born for the fabrication of aesthetic and functional prototypes. Recently used for small and medium series of parts and for tooling, it received particular attention in order to integrate prototyping systems within production. A limiting aspect of this technology is the obtainable roughness and above all its prediction: no machine software and Computer-Aided Manufacturing implements a relationship between process parameters and surface quality of components. The prediction of the surface properties is an essential tool that allows it to comply with design specifications and, in process planning, to determine manufacturing strategies. Recently, great effort has been spent to develop a characterization of such surfaces. In this chapter, prediction models are presented and a new characterization approach is detailed. It is based on the theoretical prediction of the geometrical roughness profile, thus allowing it to obtain, in advance, all roughness parameters.

Design and Selection of Chemically Deposited Ni-P-W Coatings for Optimum Tribological Behavior

Chemically deposited nickel coatings possess superior tribological properties such as high hardness, good wear, and corrosion resistance. The quest for improved tribological performance has led to the design and selection of newer variants of these coatings. The present chapter deals with the development of Ni-P-W coating on mild steel substrate and the improvement of tribological characteristics through modification of the coating process parameters. Three coating process parameters, concentration of nickel source, concentration of reducing agent, and concentration of tungsten source along with the annealing temperature, are optimized for minimum friction and wear of the coating. Friction and wear tests are carried out in a multi-tribotester using block on roller configuration under dry conditions. Taguchi-based grey relational analysis is employed for the optimization of this multiple response problem using L27 orthogonal array. Analysis of variance shows that the concentration of nickel source, the interaction between nickel source concentration, and reducing agent concentration, and also the interaction between nickel source concentration and tungsten source concentration have significant influence in controlling the friction and wear behavior of chemically deposited Ni-P-W coating. It is observed that wear mechanism is a mild adhesive in nature. The structural morphology, composition, and phase structure of the coating are studied with the help of Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray analysis (EDX), and X-Ray Diffraction analysis (XRD), respectively.

Functional Surfaces in Mechanical Systems

This chapter deals with functional surfaces in mechanical systems. These surfaces are named in a multitude of ways; therefore, a classification is provided based on how the texture is designed. For a better clarification, a number of practical examples for each category are given. An overview of fabrication methods employed to produce such surfaces is presented. The numerous fabrication methods are classified based on the mechanism they employ for providing a texture. Three main categories (removing, moving, and adding material techniques) are identified, and for each of them, a number of processes are described with examples of the textures they can create. The last section of the chapter deals with surface metrology, a topic of central importance in the design and generation of surfaces for functional purposes. The process of surface characterisation is outlined, reviewing measuring instruments, classical and advanced filtering procedures, quantification methods, and eventually, providing traceability considerations.

Surface Modification and Structure Control for Nano- and Fine-Particle Aggregation and Adhesion Behaviour Control in Liquid Phase

Two kinds of approaches for preparing surface-modified nanoparticles, such as post-synthesis surface modification and in-situ surface modification, are introduced in this chapter. Post-synthesis surface modification involves the surface modification of manufactured nanoparticles. The in-situ process involves surface modification during the nanoparticle synthesis. For a non-DLVO-type surface interaction, such as a steric or bridge force, a colloid probe Atomic Force Microscope (AFM) is useful for analysing the dispersion behaviour of the nanoparticles. Some examples of the relationship between the surface interaction and the dispersion behaviour of nanoparticles are introduced to develop the interface structure design.

Laser Additive Manufacturing in Surface Modification of Metals

Additive Manufacturing (AM) offers lots of advantages when compared to other manufacturing processes, such as high flexibility and ability to produce complex parts directly from the Three Dimensional (3D) Computer-Aided Design (CAD) model. Producing highly complex parts using traditional manufacturing processes is difficult, and it requires it to be broken down into smaller parts, which consumes lots of materials and time. If this part needs to have a surface with improved property or a surface made of composite materials, it has to be done by employing another manufacturing process after the parts are completed. AM, on the other hand, has the ability to produce parts with the required surface property in a single manufacturing run. Out of all the AM technologies, Laser Additive Manufacturing (LAM) is the most commonly used technique, especially for metal processing. LAM uses the coherent and collimated properties of the laser beam to fuse, melt, or cut materials according to the profile generated from the CAD image of the part being made. Some of the LAM techniques and their mode of operations are highlighted in this chapter. The capabilities of using LAM for surface modification of metals are also presented in this chapter. A specific example is given as a case study for the surface modification of titanium alloy (Ti6Al4V) with Ti6Al4V/TiC composite using laser material deposition process – an important LAM technology. Ti6Al4V is an important aerospace alloy, and it is also used as medical implants because of its corrosion resistance property and its biocompatibility.