There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

The MN+1AXN phases: A new class of solids

Welding Metallurgy of

Pulse and pulse reverse plating—Conceptual,advantages and applications

Over the last 40 years, the commercial production of titanium and its alloys has increased steadily. Whilst these materials have some very attractive properties, enabling applications in many industries, they are seldom used in mechanical engineering applications because of their poor tribological properties. This paper starts with an introduction to the titanium material and a review of the different types of surface treatment. The processes of nitriding, oxidation and carburizing are among the most popular thermochemical treatments aiming at improving the surface properties of Ti-alloys. Different kinds of nitriding are investigated like plasma nitriding, ion nitriding, and laser and gas nitriding. The kinetics of nitriding and the conditions for the formation of nitrided layers are studied. The influence of the main processing parameters such as temperature, time on the microstructure and the formation of new phases during the processes of nitriding is discussed. Also based on investigations presented in the literature, the effects of nitriding on the microhardness and the corrosion resistance of titanium and titanium alloys are analyzed. The improved mechanical properties, which arise from these thermochemical treatments, are discussed in relation to the potential for applying these alloys to different industries.

Enhancing the microstructure and properties of titanium alloys through nitriding and other surface engineering methods

Intermetallic coatings produced by TIG surface melting

The results of laser nitriding of commercial purity titanium (CPTi) in diluted and undiluted nitrogen environments are described in this paper in terms of surface cracking, surface hardness, hardness profile and microstructure. Surface cracking can now be totally eliminated either by nitriding in a dilute nitrogen atmosphere or by controlling the laser parameters and gas flow rate in a pure nitrogen environment. The hardness developed in a crack-free trail surface produced in a dilute nitrogen environment was less than half of the maximum hardness that can be attained using pure nitrogen. The surface hardness after glazing in a dilute environment was dependent on the nitrogen concentration in the mixture, and increased with increasing nitrogen content. The nitrided layer generated in a dilute environment possessed a fine needle-like structure, the needle size increasing with increasing nitrogen concentration in the gas mixture. In a pure nitrogen environment the nitrided layer possessed a dendritic structure of titanium nitride. The trail surfaces were found to be relatively smooth when nitrided at 50 mm s− using 2.8 kW laser power with a 5 mm defocused distance.

Crack-free hard surfaces produced by laser nitriding of commercial purity titanium

The creation of wear resistant surface metal matrix composites in both aluminium alloys and titanium via the incorporation of preplaced SiCp has been successfully undertaken by using a 5 kW CO2 laser. The problems associated with the production of a metal matrix composite layer freefrom porosity, cavities, and cracks, with a satisfactory distribution of ceramic were considered. Optimum laser processing conditionsfor Al–SiCp gave a well distributed ceramic withfew defects, but limited to 35 μm thickness. This was increased to 250 μm using a preplaced mixture of Al powder and SiCp. A prep laced SiCp layer on commercially pure Ti resulted in a dissolution of SiCp and precipitation of TiC, or the partial dissolution of SiCp and agglomeration into a hard layer (1400 HV). Pin on disc wear tests indicated that surfaces could be produced via laser surface melting associated with preplaced SiCp which showed a similar wear resistance to bulk metal matrix composite Al alloy–SiCp, and an improvement of an or...

Shahjahan Mridha

Papers

Intermetallic coatings produced by TIG surface melting

Crack-free hard surfaces produced by laser nitriding of commercial purity titanium

Design of surface in situ metal–ceramic composite formation via laser treatment

Titanium nitride layer formation by TIG surface melting in a reactive environment

Effects of nitrogen gas flow rates on the microstructure and properties of laser-nitrided IMI318 titanium alloy (Ti–4V–6Al)