# Investigation of CuTi Alloy for Applications as Non-Sparking Material
## 3 Results and Discussions
### Microhardness and Coefficient of Friction Analysis of Cu\({}_{2}\)Ti and Cu\({}_{3}\)Ti Alloys  
Cu is also alloyed with various elements, in this case Ti, to modify the relatively reduced mechanical properties of pure Cu. For alloys proposed for industrial applications other than electrical or electronic, copper alloying is absolutely necessary. In this sub-section, certain mechanical characteristics of the Cu\({}_{2}\)Ti and Cu\({}_{3}\)Ti alloys have been monitored and analyzed, as well as the surface condition of the alloys after hot spark tests in an explosive atmosphere. To determine the mechanical characteristics, the calculations are based on the plastic flow rules, as proposed in [PERSON]'s pioneering work [31; 32; 33], and only the unloading part of the load-displacement curve was used to determine the elastic characteristics such as the Oliver-Pharr methods [34; 35] and Doerner-Nix [36; 37; 38], these functions are integrated into the indentation equipment used in these determinations. These two methods assume that the onset of unloading is elastic. The above two methods propose different means of evaluating the Needle (the contact area observed at full load), leading to an efficient and practical way to evaluate the Young's modulus characteristic of solid materials, and in most cases, an estimate can be made with an error of less than 10% [39; 40]. Cu has a [PERSON]'s ratio of 0.33 and Ti between 0.265 and 0.34, and in calculating the [PERSON]'s modulus a value of 0.33 was used for the [PERSON]'s ratio [41]. In Figure 8a, a schematic representation of the entire mechanical work during the indentation procedure is shown. The portion of the area below the creep zone between Cmax_0 and Cmax quantifies the part of the energy dissipated during constant application of the maximum load Fz_max. The time taken to apply the load depends on the method used. The load-discharge curves show a similar appearance for the alloys studied, with different values obtained as a result of their response. From the graphs shown in Figure 8b, it can be noted that in all cases the areas representing the plastic mechanical work are higher than those representing the elastic mechanical work. As for the creep rates, the values have a decreasing trend from cast Cu\({}_{2}\)Ti to cast Cu\({}_{3}\)Ti and to rolled Cu\({}_{2}\)Ti (the indicative values taken from the charge-discharge graphs were 126 nm to 115 nm and 108 nm, respectively). The main values from different areas of the samples, as well as the average values (Table 4), show similar hardness values, with small differences between areas or even between alloys, the highest value being obtained for the cast Cu3 Ti alloy and the lowest for the rolled one. Larger differences were observed for [PERSON]'s indentation modulus  
Figure 8: Schematic representation of plastic, elastic and creep components of indentation for indentation curves (loading/unloading) as a function of applied force and displacement in (**a**) and in (**b**) experimental micro-indentation curves of cast Cu\({}_{2}\)Ti, Cu\({}_{3}\)Ti alloys cast and rolled Cu\({}_{3}\)Ti. (a measure of the stiffness of an elastic and isotropic material), primarily an almost doubling of the indentation modulus by increasing the mass percentage of Ti from 2 to 3 wt %. By adding more than 2% Ti, confirmed by structure and phase tests, due to the formation of a higher number of intermetallic and intracrystalline compounds, for example, TiCu4, an increase in the microhardness of the alloy from 1.6 to 1.7 GPa is observed, which corroborated an increase in the indentation modulus from 52 to 96 Gpa. Based on the existence of a linear relationship between hardness and toughness, increasing the Ti content in an alloy causes its hardness to increase sharply, but this will negatively affect its plasticity. As the number of passes increases in the hot rolling process, hardness, modulus of elasticity and contact stiffness increase, while depth and contact area vary slightly.