Microstructure of TiN coatings synthesized by direct pulsed Nd:YAG laser nitriding of titanium: Development of grain size, microstrain, and grain orientation

Abstract

Pure titanium was irradiated by pulsed Nd:YAG laser irradiation in nitrogen atmosphere. As a result, nitrogen uptake and diffusion occurred and a TiN layer was synthesized at the titanium surface. These TiN coatings were analyzed by X-ray diffraction and the diffraction patterns were investigated in detail, in order to obtain more information about the physical processes during the coating formation. The diffraction peaks were fitted by Pearson VII profiles and the grain size and the microstrain were determined by the analysis of line broadening and peak shifts, using the Williamson-Hall and the Warren-Averbach formalisms. Additional single-line analyses were performed by means of the method of Langford and Keijser to obtain information about the preferred grain orientation and the texture development. The maximum grain size was about 100 nm and a corresponding average lattice strain of 0.002 was found. A relation between the treatment parameters and the coating properties, such as grain size and microstrain, can be shown. Thus, it was possible to determine optimal scan parameters for material processing and to establish the physical limits of the coating properties.PACS 81.65.Lp; 81.15.Fg; 61.10.Nz; 68.55.Jk IntroductionNitriding and carburizing of metals are well known techniques to improve the tribological properties like hardness and wear resistance of technical surfaces [1]. As an example, plasma-and gas nitriding are established methods for surface treatment [2,3]. Alternatively, it is possible to treat the surface with laser radiation and to directly synthesize hard coatings [4][5][6][7][8]. Previous works have shown the successful synthesis of titanium nitride with laser irradiation [9][10][11]. Here, a Q-switched Nd:YAG laser was used for the nitriding treatment. The main advantages of this method are a reduction of the processing time and the negligible heat load for the workpiece. Stress, microstrain and inhomogeneity remain the main problems. Also the texture of cubic titanium nitride is a decisive factor for the technical quality of the coatings, as the u Fax: +49-551-39-4493, E-mail: pschaaf@uni-goettingen.de texture influences strain development and finally crack formation and propagation. Some investigations on texture and strain development in relation to the process parameters have been reported in the literature [12][13][14].This work resolves the resulting grain size and strain development and relates them to laser treatment parameters like scan parameters. In this way, one can try to predict optimum treatment parameters for optimum coating properties, i.e. find parameters that minimize the lattice strain in order to reduce crack formation and propagation. Experiments 2.1 Sample treatmentConventional α-titanium (purity > 99.98%) was used for the treatments. Titanium sheets of 1 mm thickness were cut into pieces of 15 × 15 mm 2 and used in the asreceived state without any further treatment.For laser nitriding, the samples were placed in a chamber which was first evacuated and then fil...

TiN-coating formation by pulsed Nd:YAG laser irradiation of titanium in nitrogen

“…Crystallite size and microstrain are resolved elsewhere. 22 Nitrogen depth profiles Diffusion-like nitrogen contents are shown in Figs. 4 and 5.…”

Revisión sobre nitruraciones láser de aleaciones de titanio

“…La mayor parte de las nitruraciones láser, llevadas a cabo por diversos investigadores, han empleado el láser de CO 2 como fuente de energía [17][18][19][20][21][22][23][24][25][26][27] . En algunos casos, se realizan procesos de nitruración utilizando un láser Nd:YAG [28][29][30][31][32][33] . El láser de diodo se ha utilizado también para la nitruración de una aleación intermetá-lica de Ti-Al [34] y para la nitruración de la aleación Ti-6Al-4V [35] .…”

Laser nitriding: investigations on the model system TiN. A review

“…In recent publications [17][18][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63]] the preparation of the treatments was always the same. Setups from other authors were similar to that one and just vary in parameters and geometry.…”

“…Nd:YAG laser nitriding The Nd:YAG laser used in [57][58] operates in the first harmonic and is equipped with an optical scanner, which allows diverse relative movements of the beam. The Scans were accomplished in a meandering fashion like described before.…”

“…In the first part the synthesis of TiN coatings using Nd:YAG laser gets instructed. The results were taken from own investigations [57][58] and the literature [42-48, 51, 70-81] . The second part will discuss the process utilizing a free electron laser, a unique heat source with a special time structure.…”