Fireside corrosion and erosion of heat exchanger tubes is a serious problem. One of the methods to combat this is by applying corrosion and erosion resistant coatings. Nickel– chromium alloys have already been used as coatings to deal with oxidation environments at high temperature. The wear resistance of these coatings can be improved by adding different hard precipitates such as carbides of refractory metals and cemented carbides. In the present study, various compositions comprising of Ni-Cr with 15, 35, 60 and 100% wt% WC/Co were made using thermal spray grade powders. These were then coated on steel substrate by the HVOF method. After detailed characterization of the coatings, the performance of the coatings at high temperature was studied by exposing the coated samples in the temperature range of 600-700°C. Ni-alloy coatings with moderately (15%) added WC/Co showed better oxidation resistance than coatings with high percentage of WC/Co and also than the pure Ni-alloy coating in high temperature range of 600-800°C. From the characterization, it was found that Ni-Cr alloy with 15% WC/Co gave the optimum results.

This work investigates the effect of processing parameters on the microstructure and composition of Ni-base alloys produced by laser forming, an additive technique also known as direct metal deposition. The parameters assessed in the study include powder flow rate, traverse speed, laser power, and spot size. In all experiments, a melt pool diameter of 0.3 mm was maintained. The results show that laser formed alloys are similar in structure to conventional wrought alloys with additional peaks formed as a result of the oxidation of active alloying elements. The complex compounds observed on the surface of the laser formed samples disappeared after polishing. Paper includes a German-language abstract.

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 such as AISI Type 304 SS are being used for seawater piping applications due to their desirable mechanical properties and good weldability. However, they are susceptible to pitting and crevice corrosion in chloride bearing environments. Thus a new generation of highly alloyed stainless steels such as Avesta 254 SMO with high molybdenum contents has been developed for improved localised corrosion resistance in seawater. These steels are also susceptible to the formation of undesirable secondary phases such as sigma and chi which degrades both mechanical and corrosion properties. Alternatively, the main alloying element can be surface alloyed onto the surface of a suitable substrate by laser surface alloying. In this paper, austenitic stainless steel surface alloys of varying molybdenum contents have been formed on 304 SS by laser surface alloying and characterised by optical and scanning electron microscopy. The corrosion behaviour was ascertained by electrochemical and immersion tests.

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.