High repetition rate femtosecond laser heat accumulation and ablation thresholds in cobalt-binder and binderless tungsten carbides

Abstract

Femtosecond (fs) laser ablation has been studied for the potential of fast, high precision machining of difficult-tomachine materials like binderless tungsten carbide. Obstacles that have limited its efficiency include melting from heat accumulation (HA), particle shielding, and plasma shielding. To address HA without shielding effects, high repetition rate (57.4 MHz), ultra-low fluence fs laser irradiation is performed to study the incubation effect and subsequent HA-ablation threshold of fine-grained tungsten carbides. Exposure times on the order of 100 ms were conducted in air with fluences (1.82 to 9.09 mJ/cm 2 ) two orders of magnitude below the single fs pulse ablation thresholds reported in literature (0.4 J/cm 2 ). Heat accumulation at high repetition rate explains the ultra-low fluence melt threshold behavior resulting in melt crowns around ablated holes and grooves. The results of this study aid in predicting heat buildup in high repetition rate laser irradiation for applications that wish to achieve high ablation rates of difficult-to-machine, ultrahard materials and help enable shaping of binderless tungsten carbide for use in applications too extreme for bindered tungsten carbide.

Ultrafast laser ablation of tungsten carbide: Quantification of threshold range and interpretation of feature transition

“…P2 was situated away from the laser center and was ablated at stage II; the temperature of P2 increased continually from the room temperature to the boiling temperature with the accumulation of pulses, indicating that the unablated material at stage I could be ablated later when the pulse number reached a certain level. P3 was located at the bulge adjacent to the edge of crater; the temperature of P3 rose initially increased but generally stayed below the boiling temperature no matter how many pulses were added; materials here could be heated and softened instead of being ablated 25 ; the softened materials were subsequently extruded under the laser impact force and counterforce from laser‐induced evaporation and ionization, 26 as shown in Figure 3D. P4 was located away from the ablated crater but could also be irradiated by laser; temperature of P4 stayed below the melting point no matter how many pulses were accumulated, preventing material at this location from being ablated; however, the oxidation and decomposition were induced under this condition, 27 which was analyzed in detail later in this manuscript.…”

Femtosecond Laser Induced Surface Damage and Ablation of Tungsten and Tungsten Carbide in High Heat Flux Conditions

“…Analogous laser-materials interactions occur on cemented tungsten carbide samples during femtosecond laser ablation in ambient air. Here the heat transfer time delays to 2.8μs [12]. Laser induced plasma delivers energy to surface of materials that can recreate the heat loading.…”

“…Tungsten carbide has been widely used for cutting and machining due to its good wear resistance, high hardness, and melting point of 2870℃. Usually, a cobalt binder in the matrix improves the formability of the material and microstructures in the material become a cement phase [ 12 ]. Tungsten carbide as a hard material has been tested elsewhere to see the heat induced surface damage from an electron beam [ 13 , 14 ], nanosecond [ 15 ] and femtosecond lasers [12].…”

“…Usually, a cobalt binder in the matrix improves the formability of the material and microstructures in the material become a cement phase [ 12 ]. Tungsten carbide as a hard material has been tested elsewhere to see the heat induced surface damage from an electron beam [ 13 , 14 ], nanosecond [ 15 ] and femtosecond lasers [12]. The tungsten carbide ablation threshold is estimated to be 0.4J/cm 2 [ 16 ].…”

Ultra-Short Pulse Laser Cleaning of Contaminated Pleistocene Bone: A Comprehensive Study on the Influence of Pulse Duration and Wavelength

“…In comparison to nanosecond pulsed lasers, ultrashort laser pulses exhibit intense nonlinear interactions with matter as one of their most striking features [32,33]. The comparatively low thermal load generated by ultrashort laser pulses on the substrate reduces any collateral impact caused by heat accumulation [34,35], such as burning, cracking, and thermally induced chemical changes. Additionally, the nonlinearity of the interaction makes it possible to remove nanometric thin layers of material with great precision and control [27,36].…”