This paper discusses the challenges of constructing mathematical models of physicochemical and heat-mass transfer processes associated with reactive heterogeneous materials used in laser additive manufacturing. The results of calculations of thermocapillary convection induced by laser heating in an aluminum melt with an admixture of nickel particles are presented. Models of interphase and chemical interactions with the formation of intermediate phases and intermetallic compounds on nickel particles added to the melt during laser alloying or cladding are proposed, which make it possible to calculate the composition of intermetallic phases in the trace of the beam after crystallization and cooling.

In this work, numerical modeling is used to simulate the effects of laser remelting as a post treatment and as an in-situ component of a hybrid plasma spraying process. Initially, a single-pass 2D model is used to simulate the laser post-treatment process in order to obtain relationships between melting pool depth, relative scanning velocity, and laser power. A 3D finite-element model is then used to study temperature variations during multi-layer deposition of a NiCr alloy by plasma spraying with in-situ laser melting. The effects of phase change are taken into account by defining the enthalpy of the material as a function of temperature. Predicted melting pool depth corresponded well with experimental values.

Titanium alloys are used in several fields due to their outstanding high specific strength, low density and excellent corrosion resistance, but the low wear resistance confines their applicability. The performance of CVD and PVD coatings is limited by the low hardness of the substrate, which cannot supply sufficient support, and conventional thermal spray coating materials do not provide the excellent corrosion properties. Laser alloying also often results in a decreased corrosion resistance and additionally in embrittlement. The use of boron for laser alloying or dispersing of diborides permits the incorporation of extremely hard boride phases without significant decrease of the matrix materials corrosion resistance and ductility, as there is no solubility of boron in titanium. Laser alloying with boron paste and dispersing of TiB 2 in Ti6Al4V surfaces is carried out with CO 2 lasers and an adapted inert gas shower apparatus. Typically a melt pool depth of 200 - 300 µm is achieved and the boride precipitates permit an increase of the surface hardness from 350 HV0.05 in the initial state to about 800 HV0.05. The surface area is characterized by means of optical microscopy, SEM and EDXS. Vacuum plasma spraying is used to provide a technology for deposition of TiB 2 layers with defined thickness prior to laser treatment on surfaces with complex shape and in order to evaluate the direct applicability of thermally sprayed TiB 2 coatings.

Lightweight materials such as Al and Ti alloys tend to show poor wear resistance. However, laser alloying of thermally sprayed coatings can be used to form intermetallic phases within the surface area to overcome this disadvantage and to build a metallurgical bond between substrate and coating. Such phases formed in an exothermic reaction may show excellent corrosion behaviour and wear resistance. These reactions can be used to influence the surface properties by remelting metallic coatings on Al or Ti substrates. With respect to the wear behaviour, Ti and Al intermetallics are of great interest. Ti and Al alloys were coated by Al, Ti, and Ni respectively. The different structures on the surface of the alloys depend first on the laser processing parameters resulting in the overheated melt and as well as the latent heat of the formed intermetallic phases. The experimental results clearly show that for short dwell times the latent heat dominates the solidification process and that at high solidification rates the microstructure formation becomes nearly independent from the process parameters. This effect is of special interest for industrial applications as quality requirements ask for robust processes. The paper discusses the metallurgical fundamentals of intermetallic phases and the energy balance of the solidification while giving a deep insight into the influence of different process parameters. Lastly, the properties of alloyed surfaces are discussed.

Borides are promising materials with good wear and corrosion resistance properties. Boride coatings are expected to perform better where wear and corrosion resistances are simultaneously required. Zirconium diboride is an important emerging material for such applications, due to its high hardness, high melting point, good wear resistance and corrosion as well as high temperature oxidation resistance. Special properties of laser beam like beam directionality, high intensity and spatial resolution makes laser alloying a fast and efficient technique for producing improved wear resistance coatings. In the present work, mild steel was laser alloyed with ZrB2, using "two-stage" technique of laser alloying. These coatings after characterization by optical microscopy, SEM, EDAX and XRD techniques were tested on a "Pin-on-Disk" machine for determining their wear resistance.

Stainless Steels are required for many applications for ship building as well as for offshore structures such as oil exploration. AISI type 304 stainless steel is not very suitable for such applications as it has a strong tendency for pitting and crevice corrosion. Even type 316 and 317 stainless steels which have respectively 2.5 and 3.5% Mo are not very effective in these environments. Commercially available stainless steels, viz., Avesta 254 SMO is being employed for such applications because of its strong resistance to pitting and crevice corrosion. This is mainly because of high Mo concentration (6.5%). Such steels are not only costly but are prone to form deleterious phases such as delta ferrite and sigma during welding or other heat treatment operations. Hence, an alternative technique to restrict Mo at the surface is needed. In the present work, surface alloys consisting of an austenitic stainless steel with Mo content as high as 10-12% have been formed on stainless steel type 304 substrates. These steels show enhanced passivity and strong resistance to pitting corrosion.