William Dallas Sproul

Young's modulus of TiN, TiC, ZrN and HfN☆

Abstract The Youngs modulus of group IVB nitride and TiC films coated onto stainless steel substrates by reactive sputtering has been derived from their flexural resonance frequemcy. The values found for stoichiometric ZrN and HfN are 460 GPa and 380 GPa respectively. A wide range of TiN compositions was studied: the modulus increases steadily with nitrogen level to be about 640 GPa at the stoichiometric composition. A limited number of TiC samples has been measured; taking existing literature values into account a value for the stoichiometric phase of 460 GPa is derived.

Very high rate reactive sputtering of TiN, ZrN and HfN☆

Abstract The reactive sputtering rate for the group IVb nitrides approaches the sputtering rate for the metal provided that there is precise control of the process parameters. For TiN the reactive sputtering rate is 100% of the metal rate whereas for ZrN and HfN the rate is 95% of the metal rate. Compared with chemical vapor deposition and other physical vapor deposition processes, reactive sputtering of these compounds is a low temperature process. The maximum recordable substrate temperature immediately after deposition was 315 °C. The hardness of the TiN and ZrN coatings is greater than the bulk value, and the adhesion of these coatings to M2 steel is excellent. Cutting tool tests showed that TiN coatings reactively sputtered at a high rate are very effective in enhancing tool life.

High rate reactively sputtered TiN coatings on high speed steel drills

Abstract TiN can be reactively sputtered at the full metal deposition rate and still achieve excellent properties. The TiN coatings have a (111) preferred orientation and a lattice parameter of 0.424 nm. The coating hardness is 2490 kgf mm -2 for a coating 1–2 μm thick. TiN-coated drills were tested under accelerated machining conditions. The speed and feed were chosen such that an uncoated drill failed in two or three holes while drilling dry a hole 1.25 cm deep in 4130 steel hardened to 235 HB. The speed was 1150 rev min -1 and the feed was 0.21 mm rev -1 . Under the same conditions, the TiN-coated drills averaged 150 holes before failure. Cutting fluids either helped or hindered coated cutting tool life. One soluble oil cutting fluid increased the coated tool life to 301 holes whereas another decreased life to only ten holes. For a second set of tool life tests, M-7 high speed steel drills were coated by two different commercially available physical vapor deposition (PVD) processes (A and B) and by the high rate reactive sputtering process. The drills were run at 2300 rev min -1 with a feed of 0.11 mm rev -1 with a water-soluble cutting fluid. The workpiece was 4340 steel hardened to 285 HB, and the hole depth was 1.25 cm. Drills coated by PVD process A had an average life of 530 holes ( S = 407); those coated by PVD process B, 398 holes ( S = 209); and the reactively sputter-coated drills, 452 holes ( S = 96). The smaller standard deviation of the sputter-coated drills means that these drills will be much more reliable in cutting applications than the other two.

High rate reactive sputtering process control

Abstract Reactive sputtering is usually a slow process because the reactive gas interacts with the target, and in this poisoned state the deposition rate drops off. Pulsing the reactive gas led to improvements in the reactive deposition rate. At fast pulsing rates (0.2 s on, 0.2 s off), the reactive deposition rate for TiN is almost the same as that for metallic titanium, but control of the process is difficult. Implementation of a closed-loop feedback control system using the nitrogen peak height (partial pressure) from a mass spectrometer as the control signal to the reactive gas mass flow controller brought the process under control and also removed the need for pulsing. The closed-loop control system is not dependent on the sputtering system pumping throughput, and it has such good control that it can move up and down the knee of the hysteresis curve without the target becoming fully poisoned. Multiple gases can also be controlled, and using a derivative of this process it is possible to compensate for the deleterious effects of water vapor outgassing during the coating run.

Variations in the reflectance of TiN, ZrN and HfN

Abstract The gold-like color and high hardness of the group IVB nitrides have allowed their use as scratch-resistant decorative coatings. The color can be varied with composition and mode of preparation. In the present work, TiN, ZrN and HfN films with different nitrogen-to-metal ratios were prepared on stainless steel by reactive sputtering. Half of each sample was vacuum annealed at 900°C for 1 h. The lattice parameters, reflectance and color were determined. The lattice parameters remained above equilibrium even after tempering. The experimental reflectance curves were analyzed in terms of the reflectance minima (between the screened Drude plasma edge and the onset of interband transitions) and the value of the reflectance at a photon energy of 1 eV (which is representative of the relaxation behavior). For all three nitrides the reflectance minimum is reduced to lower values of photon energy and reflectance as the nitrogen content is increased through the stoichiometric point. The reflectance at 1 eV increases concurrently. The degree of yellowness increases with nitrogen content, but no consistent effect of tempering could be defined. The behavior is described as the combined result of charge transfer from the metal to the metalloid atom (thus changing the effective density of conduction electrons) and of varying concentrations of vacancies and interstitials.

The chemical analysis of TiN films: A round robin experiment

Abstract Two series of titanium nitride films have been prepared under different conditions by reactive d.c. bias magnetron sputtering. They have been studied by X-ray photoelectron spectroscopy (XPS), electron probe microanalysis (EPMA), Auger electron spectroscopy (AES), X-ray diffraction (XRD) and gravimetric oxide chemical analyses, in a round robin experiment, to compare the reliability of the techniques in characterizing films quantitatively. The EPMA, AES and chemical analyses (where applied) of the samples produce consistent data. However, a discrepancy was found between AES and XPS data in one series of samples. XRD shows considerable deviations from equilibrium in the lattice parameters, negating its use in analysis.

Turning tests of high rate reactively sputter-coated T-15 HSS inserts☆

Abstract T-15 high speed steel cutting tool inserts were coated with TiN, TiC, ZrN, ZrC, HfN and HfC by high rate reactive sputtering, and these coated inserts were tested in two high speed lathe turning tests. All coated inserts outperformed uncoated ones, and TiN coated inserts had the longest life in both tests. With 4340 steel as the workpiece, the order of performance of two-step coated inserts in descending order was TiN, TiC, ZrC, HfC, ZrN and HfN. In a less abrasive cutting test with 1045 steel as the workpiece, the order of performance of angle-coated inserts was TiN, HfC, ZrN, HfN, TiC and ZrC.

Solid solution hardening in high rate reactively sputtered (Hf, Ti)N coatings

Abstract Coatings of (Hf, Ti)N were deposited by a high rate reactive sputtering process using a dual-cathode configuration. The coatings were analyzed to determine the effect of film composition of microhardness. Solid solution hardening was observed and was dependent on the partial pressure of the reactive gas (N 2 ). At the pressure where hardening was observed, the maximum hardness (3760 HV at 100 gf) occurred at a Ti:(Ti + Hf) ratio of approximately 50%.

Wear of sputter deposited refractory‐metal nitride coatings

Reactive sputtering of a metallic compound normally is a slow process. A compound forms on the surface of the target, and the sputtering rate of the compound is much slower than that for the pure metal. With dc magnetron sputtering in an Ar/N2 atmosphere, it is possible to operate at the knee of the hysteresis curve and reactively form TiN, ZrN, and HfN on the substrate at very high deposition rates provided that there is precise control of the reactive gas. TiN is reactively sputtered at 100% of the metal deposition rate, whereas for ZrN and HfN the rate is 95% of the metal rate. Stoichiometric as well as non‐stoichiometric compounds can be formed, and the color of these coatings varies with nitrogen content. TiN, ZrN and HfN have the NaCl structure and show a (111) preferred orientation. Stoichiometric sputtered TiN and ZrN have the same lattice parameter as the bulk material, but sputtered HfN has a larger lattice parameter. The residual stresses in these nitride coatings are compressive, and all three...