Titanium aluminides are used in the aeronautical and automotive field as an alternative material to manufacture critical components exposed to high temperatures and corrosive environments. These alloys due to its intermetallic structure exhibit some special properties such as low density, high strength, high stiffness, corrosion resistance, and creep resistance. When these components are manufactured, surface integrity is one of the most relevant parameters used to evaluate the quality of the parts. Severe surface integrity problems are reported in the literature, defects such as microstructural alterations, work hardening, residual stresses, surface cracks, among others induced by the cutting process. The surface and sub-surface alteration induced by machining are critical because it will affect the parts performance. Some parameters affect the quality of machined surface. In particular cutting parameters, cutting tools material, tool wear and material properties are the most frequently investigated. Experimental and empirical studies are presented mainly in order to understand the surface integrity induced by machining. This paper provides an overview of the problems associated with the machining process of various types of titanium aluminides. The cutting tools, machining parameters, as well as processing parameters employed to improve machinability and reduce surface defects in titanium aluminides are analyzed and discussed. Particular focus was given to turning and milling process of gamma titanium aluminides. Also, some of the optimal parameters for machining titanium aluminides are presented offering a compilation of the most relevant information from the first to the most recent works that analyze the different aspects that affect the machining of these alloys.

The international safety regulations are pushing the manufacturers of water systems and equipment to remove lead from material compositions due to the potential human hazard of lead absorption. The usage of green lead-free brass alloys is becoming mandatory in many important markets, demanding the manufacturers to quickly adapt their production techniques both casting and machining to this new reality. Regarding machining, lead has been used to facilitate the chip control, working as a natural chip breaker and reducing the tool wear. Therefore, the reduction of lead composition in brass alloys contributes to a machinability decrease of the materials leading to higher cutting forces, long chips and higher tool wear. This work focuses on the machinability characterization of three different brass alloys (leaded, medium-leaded and minimally leaded) by means of cylindrical external turning process with polycrystalline diamond inserts. A parametric study covering three different depths of cuts, three feed rates and four cutting speeds was conducted for three brass alloys with two repetitions. Cutting forces, chip morphology and surface roughness were analysed and compared between alloys. Complementary microstructural and mechanical characterization of the alloys were performed. Analysis of variance was performed to analyse the results. Cutting forces, power consumption, specific cutting pressure, roughness and chip morphology identification were used as comparison criteria among the tested materials. Results have demonstrated the decrease of machinability with the lead reduction, with higher cutting forces and longer chips. Polycrystalline diamond tools used in this work could be a good option to overcome the machinability challenges of the lead-free brass alloys.

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