HfN Coatings Research Articles

Improvement of structures and properties of hafnium nitride coatings by yttrium introduction

In recent years, rare earth element doping has become an important emerging way to improve material properties. In this study, the effects of rare earth Y doping on the morphology, microstructure and properties of Hf-Y-N composite coatings were analyzed by combining equipment characterization methods and simulation methods. The results showed that when the content of Y was 9.8 at.%–18.5 at.%, (Hf, Y) N substituted solid solution was formed by Y atoms replacing Hf atoms. And as the Y content increased, the lattice distortion of coatings increased and the grain size decreased. The maximum hardness of the coating was 34.6 GPa when the doping amount of Y was 18.5 at.% and the hardness values of the Hf-Y-N composite coatings were greater than those of the binary HfN coatings. The fracture toughness of the composite coatings increased with the increase of Y doping content. The maximum fracture toughness was 4.8 MPa. m1/2, which was nearly five times higher than the fracture toughness of binary HfN coatings. The solid solution strengthening and fine grain strengthening effects caused by the doping of Y were responsible for that. At the same time, the adhesion between the coatings and the substrate was significantly improved. In addition, the doping of Y improved the thermal stability and corrosion resistance of the coating, and the corrosion current density of Hf-Y-N coating increased by two orders of magnitude compared to substrate, with a minimum of 4.21 × 10−8 A ∙ cm−2.

Ablation behavior of a novel carbonitrides HfC0.68N0.32 coating for C/C composites in laser and oxyacetylene environment

A HfC0.68N0.32 solid solution coating was synthesized on the surface of C/C composites by chemical vapor deposition (CVD). The mechanical properties and ablation resistance of HfC0.68N0.32 coating were investigated under laser and oxyacetylene conditions. Results indicated that HfC0.68N0.32 coating exhibited higher hardness and elastic modulus than HfC and HfN coatings. The phase separation of HfC0.68N0.32 coating generated in the laser ablation environment with power of 800W, and the mass ablation rate was 0.17mg/s after ablation for 10s. Furthermore, the surface temperature of the coated sample reached 2600 ℃ under an oxyacetylene environment with a heat flux density of 4.2MW/m2, resulting mass and linear ablation rates of 0.34mg/s and 0.23 μm/s respectively after ablation for 100s, showing a great potential in the field of ultra-high temperature ablation protection.

Characteristics of HfN coatings by inductively coupled plasma-assisted magnetron sputtering

For deposition technology using plasma, it plays an important role in improving coatings deposited with high ionization rate through high density plasma. Various deposition methods such as high-power impulse magnetron sputtering and ion-beam sputtering have been developed for physical vapor deposition technology and are still being studied. In this study, it is intended to control plasma using inductively coupled plasma (ICP) antennas and use properties to improve the properties of coating film using ICP-assisted magnetron sputtering (ICPMS). This sputtering method presents characteristics such as denser and smoother microstructure, better mechanical properties, etc., because it enables low temperature processes and high ionization rates at low energy. Further, The crystal structure of the coating film can also be controlled.

Study of nanostructured HfN coatings using layers arrangement

ABSTRACTIn the present investigation, nanostructured ceramic HfN coatings were deposited onto silicon (100) wafer by magnetron sputtering DC method, from a metallic Hf target. The deposition process followed by a similar pattern as the multilayer film deposition, using cycles with the nitrogen gas turned on for 90 s and turned off for 15 s; four sets of samples were obtained using 5, 10, 15 and 20 cycles. The X ray diffraction (XRD) identified the presence of two different cubic crystalline phases of HfN, corroborated by Rietveld analysis. The Vickers hardness test showed that the hardness values increases with more cycles, due to a higher compressive stress evaluated by Stoney formula. All samples were investigated with no visible fracture until 10 grf for the 5 cycles sample; however, no fractures were visible at all for the 15 and 20 cycle samples for that given load, instead fractures started to appear at 25grf for the 10 and 15 cycles coating. Eventually it is distinguished that, the thickness and morphology of the coatings were measured by field emission scanning electron microscopy FE-SEM. As well as, the thickness increased from 0.4 µm to almost 1.33 µm as the number of cycles also increased, where we can observe the formation of columnar growth, moreover it is possible to distinguish the formation of two different clusters which might be related to different phases.

Influence of Nitrogen Flow Rates on the Structure, Hardness, and Electrical Resistivity of HfN Coatings by DC Sputtering

shown to reach a maximum value of 20 GPa, and a minimum electrical resistivity of 6.5 3 10 8 lXcm. Furthermore, as the flow is increased, the hardness values gradually decrease (until a value of 8 GPa is reached), the fracture toughness increase (until a value of 0.3 MPam is reached), and the electrical resistivity reaches its maximum at 1.52 3 10 12 lXcm. These variations are attributed to the evolution that the HfN phase progressively undergoes from a crystal orientation at (111) to an amorphous phase. In addition, the presence of tensile stresses, which tend to favor electrical resistivity, was identified. The average RMS roughness increased from 3.76 to 10.69 nm as the nitrogen flow was increased. Finally, the Raman spectroscopy confirmed the presence of the HfN phase.

Characterization of chemical vapor deposited HfN multilayer coatings on cemented carbide cutting tools

The present study has been carried out in order to evaluate the tribological behavior of HfN-based multilayer-coated tools used for milling. The initial results of the wear behavior of multilayer HfN coatings, during the laboratory friction and wear tests conducted at room temperature against WC as tribological pair, are reported. As part of the characterization of the mechanical properties of the coatings, Vickers microindentation tests were also carried out employing loads in the range of 0.01–10 N, in order to evaluate the composite hardness of the coating-substrate systems. Information regarding the absolute hardness of the HfN and TiCN monolayer films has been obtained employing a model recently developed by one of the authors. This information is then used in order to determine the properties of the HfN/TiCN multilayer coating. It has been found that the wear volume of the single layer HfN coatings is approximately 15 times greater than the wear volume corresponding to the HfN/TiCN for the same amount of cycles.

Post-deposition reduction of internal stress in thin films: The case of HfN coatings bombarded with Au ions

Abstract The post-deposition bombardment of reactively sputtered HfN thin films with energetic (1, 2.5 and 5 MeV) gold ions to a fluence of 10 14 cm −2 resulted in a considerable reduction of high internal stresses which were estimated from the measurements of the surface curvature. The higher the energy of the gold species the lower degree of relaxation was registered. The observed phenomena are attributed here to the transport of the interstitial defects within the thermal spikes induced by bombarding HfN with Au ions. An alternative explanation of stress-reduction caused by an increase in vacancy concentration is also presented. Significant softening of HfN films after ion-beam treatment was registered by the high accuracy depth-sensing indentation method and attributed to the formation of an inter-layer of amorphous silicon, directly under the film. A structural analysis has been carried out using thin film X-ray diffraction. Nitride film resistivity was found to be slightly enhanced by bombardment with Au ions.

Some characteristics of HfN coatings on cemented carbide substrates

Industrially produced HfN coatings made by chemical vapour deposition were studied in terms of microstructure, hardness and adhesion. It was found that they have a (200) preferred orientation with lattice parameters greater than that of the stoichiometric phase. This is attributed to impurity effects. The scratch test critical load for the onset of coating removal is far higher than for other hard coatings. The mode of detachment is unique in that the coating first cracks and the crack edges then chip, leading to a type of zigzag failure within the coating and then to loss of adhesion. The results are interpreted in terms of high resistance to deformation and crack propagation. Scanning electron micrographs of typical scratch channels are presented together with the corresponding acoustic emission signals which are thought to be primarily an accelerometer effect associated with scratch channel damage.

Hafnium nitride coatings prepared by very high rate reactive sputtering

Hafnium nitride (HfN x ) coatings were prepared via very high rate reactive sputtering in an ArN 2 atmosphere over a wide range of nitrogen concentrations. The color of the coatings varied from a pale yellow at low nitrogen levels to a rich golden yellow color at the higher nitrogen levels. This color is different from the greenish yellow color for chemically vapor-deposited HfN coatings. As the nitrogen content of the films was increased, the cell size also increased, which is contrary to what has been reported for bulk HfN x . The reactively sputtered HfN x coatings have a (111) preferred orientation, and the cell size is 4.56 Å for the rich golden-colored films compared with 4.52 Å for the bulk material. In addition, the reactively sputtered HfN x coatings have an unexpectedly high Vickers hardness of 2570 kgf mm -2 (for a 1000 gf load). The bulk HfN hardness is reported to be 1600 kgf mm -2. The HfN coatings have very high compressive residual stresses, and the adhesion of these coatings to M2 tool steel, as measured by the Laboratoire Suisse de Recherches Horlogères scratch tester, is excellent.

Ion-plated HfN coatings

The microstructural characteristics of HfN deposited onto stainless steel by ion plating are discussed as functions of the deposition rate. The composition of the coatings is invariant and approximately stoichiometric. Their grain size becomes coarser at higher rates whilst the preferred orientation changes from (111) to (311). The crystal lattice is expanded and distorted and the coatings are under compressive stress in the plane of the coating.

Interrupted cutting tests of cemented carbide tools coated by physical vapor deposition and chemical vapor deposition techniques

Refractory compound coatings prolong the life of cemented carbide inserts. The structure of these coatings is vastly different when the same coating is produced by chemical vapor deposition (CVD) and physical vapor deposition (PVD) methods. TiC and HfN coatings were applied to cemented carbide tools by both CVD and PVD processes. The coated inserts were tested under interrupted cutting conditions using slotted bar tests. The CVD-coated inserts failed after a few (less than 100) cycles whereas the PVD-coated inserts lasted well past 2000 cycles without failure as did the uncoated inserts. PVD coatings have a much greater fracture toughness than CVD coatings due to their very fine-grained microstructure with a distribution of fine cavities which act as crack stoppers. In contrast, CVD coatings have a fully dense microstructure with a large grain size which does not have much fracture toughness. Another reason for the difference in behavior is the much lower deposition temperature (about 500°C) used in the PVD process as compared with the much higher deposition temperature (about 1000°C) used in the CVD process. Chemical attack of the cemented carbide substrate occurs at high deposition temperatures, thus weakening the area near the coating-substrate interface.