Selective Laser Treatment on Cold-Sprayed Titanium Coatings: Numerical Modeling and Experimental Analysis

Abstract

In this paper, a selective laser post-deposition on pure grade II titanium coatings, cold-sprayed on AA2024-T3 sheets, was experimentally and numerically investigated. Morphological features, microstructure, and chemical composition of the treated zone were assessed by means of optical microscopy, scanning electron microscopy, and energy dispersive X-ray spectrometry. Microhardness measurements were also carried out to evaluate the mechanical properties of the coating. A numerical model of the laser treatment was implemented and solved to simulate the process and discuss the experimental outcomes. Obtained results highlighted the key role played by heat input and dimensional features on the effectiveness of the treatment.

On the Improvement of AA2024 Wear Properties through the Deposition of a Cold-Sprayed Titanium Coating

“…The relative concentration of two elements (Ti, O), in the topmost layer of the cross-section, is approximately equal to the stoichiometric one for the titanium dioxide; moving to the interface with The relative concentration of two elements (Ti, O), in the topmost layer of the cross-section, is approximately equal to the stoichiometric one for the titanium dioxide; moving to the interface with The relative concentration of two elements (Ti, O), in the topmost layer of the cross-section, is approximately equal to the stoichiometric one for the titanium dioxide; moving to the interface with the aluminium substrate, the oxygen percentage decreases to characteristic values of titanium grade 2. It should be noted that the XRD analysis of the treated surface, presented by the authors in a previous paper [32], confirmed the formation of a rutile layer as well as a thick oxygen diffused zone underlying the oxidised zone. This result will be useful in the further discussion of the results.…”

“…It should be noted that the XRD analysis of the treated surface, presented by the authors in a previous paper [32], confirmed the formation of a rutile layer as well as a thick oxygen diffused zone underlying the oxidised zone. This result will be useful in the further discussion of the results.…”

Thermo-Mechanical Finite Element Modeling of the Laser Treatment of Titanium Cold-Sprayed Coatings

“…The results of the experimental analysis demonstrated the key role played by the aluminum substrate and the ratio between the coating and substrate thickness (also called thickness ratio, TR). Indeed, once the heat input provided by the laser source is fixed, the temperature is governed by the cooling action exerted by the aluminum substrate being more conductive than the titanium [14,16]. Thermal analysis of the laser surface processing pointed out that the peak temperature experienced by the surface and the cooling rate significantly influenced the formation of titanium oxides with good mechanical and wear properties and a satisfactory adhesion with the underlying untreated coating [8,14,16,17].…”

“…Indeed, once the heat input provided by the laser source is fixed, the temperature is governed by the cooling action exerted by the aluminum substrate being more conductive than the titanium [14,16]. Thermal analysis of the laser surface processing pointed out that the peak temperature experienced by the surface and the cooling rate significantly influenced the formation of titanium oxides with good mechanical and wear properties and a satisfactory adhesion with the underlying untreated coating [8,14,16,17]. In addition, the thermal model developed in the previous investigation was able to predict the formation of distinct microstructures inside the coating, pointing out a tight correlation between the estimated temperature fields and the developed metallurgical zones.…”

“…On the other hand, the high temperatures required to promote the proper reaction between the oxygen and the titanium, as well as the characteristics of the laser processing (e.g., high energy density as well as localized heat input) make it difficult to assess the optimal process parameters window. Indeed, experimental investigation revealed how the mismatching between the process parameter led to different adverse results, from ineffective treatment, where the conditions required for the formation of the rutile layer have not been accomplished, to damage to the processed specimen [14,16]. The experimental and numerical analyses also showed that the damaging of surface specimens could occur through two distinct phenomena: material loss from the irradiated surface with the subsequent formation of spherical craters along the treated track, and the formation of cracks inside the oxidized layer and at the interface between the hard oxide and the metal.…”