Stress-free Lattice Parameter Research Articles

Influence of ion irradiation-induced defects on phase formation and thermal stability of Ti0.27Al0.21N0.52 coatings

The influence of changes induced by ion irradiation on structure and thermal stability of metastable cubic (Ti,Al)N coatings deposited by cathodic arc evaporation is systematically investigated by correlating experiments and theory. Decreasing the nitrogen deposition pressure from 5.0 to 0.5 Pa results in an ion flux-enhancement by a factor of three and an increase of the average ion energy from 15 to 30 eV, causing the stress-free lattice parameter to expand from 4.170 to 4.206 Å, while the chemical composition of Ti0.27Al0.21N0.52 remains unchanged. The 0.9% lattice parameter increase is a consequence of formation of Frenkel pairs induced by ion bombardment, as revealed by density functional theory (DFT) simulations. The influence of the presence of Frenkel pairs on the thermal stability of metastable Ti0.27Al0.21N0.52 is investigated by scanning transmission electron microscopy, differential scanning calorimetry, atom probe tomography and in-situ synchrotron X-ray powder diffraction. It is demonstrated that the ion flux and ion energy induced formation of Frenkel pairs increases the thermal stability as the Al diffusion enabled crystallization of the wurtzite solid solution is retarded. This can be rationalized by DFT predictions since the presence of Frenkel pairs increases the activation energy for Al diffusion by up to 142%. Hence, the thermal stability enhancement is caused by a hitherto unreported mechanism - the Frenkel pair impeded Al mobility and thereby retarded formation of wurtzite solid solution.

Spatiotemporal Evolution of Stress Field during Direct Laser Deposition of Multilayer Thin Wall of Ti-6Al-4V.

The present work seeks to extend the level of understanding of the stress field evolution during direct laser deposition (DLD) of a 3.2 mm thick multilayer wall of Ti-6Al-4V alloy by theoretical and experimental studies. The process conditions were close to the conditions used to produce large-sized structures by the DLD method, resulting in specimens having the same thermal history. A simulation procedure based on the implicit finite element method was developed for the theoretical study of the stress field evolution. The accuracy of the simulation was significantly improved by using experimentally obtained temperature-dependent mechanical properties of the DLD-processed Ti-6Al-4V alloy. The residual stress field in the buildup was experimentally measured by neutron diffraction. The stress-free lattice parameter, which is decisive for the measured stresses, was determined using both a plane stress approach and a force-momentum balance. The influence of the inhomogeneity of the residual stress field on the accuracy of the experimental measurement and the validation of the simulation procedure are analyzed and discussed. Based on the numerical results it was found that the non-uniformity of the through-thickness stress distribution reaches a maximum in the central cross-section, while at the buildup ends the stresses are distributed almost uniformly. The components of the principal stresses are tensile at the buildup ends near the substrate. Furthermore, the calculated equivalent plastic strain reaches 5.9% near the buildup end, where the deposited layers are completed, while the plastic strain is practically equal to the experimentally measured ductility of the DLD-processed alloy, which is 6.2%. The experimentally measured residual stresses obtained by the force-momentum balance and the plane stress approach differ slightly from each other.

Electron irradiation induced modifications of Ti(1-x)AlxN coatings and related buffer layers on steel substrates

Ti(1-x)AlxN hard coatings were prepared by reactive magnetron sputtering onto steel substrates (51CrV4 – 1.8159) and subsequently exposed for a short-time (~1 s) to high-flux electron beam (EB) treatment. Morphology, composition and the structure of as-deposited and EB treated coatings were investigated using transmission electron microscopy (TEM), secondary ion mass spectroscopy (SIMS) and X-ray diffraction (XRD). It was found that the EB treatment had only a minor influence on the morphology and crystallinity of the Ti(1-x)AlxN phase, however, the stress-free lattice parameter and partly the compressive stress in the coatings were clearly reduced by the treatment. On the other hand, major changes of composition profiles and structure were observed in the metallic buffer layer between substrate and Ti(1-x)AlxN. The observed modifications in the coating-substrate system are explained by rapid heat up and radiation damage due to the fast electron exposure.

Gradient of Residual Stress and Lattice Parameter in Mechanically Polished Tungsten Measured Using Classical X-rays and Synchrotron Radiation

In this work, the stress gradient in mechanically polished tungsten sample was studied using X-ray diffraction methods. To determine in-depth stress evolution in the very shallow subsurface region (up to 10 μm), special methods based on reflection geometry were applied. The subsurface stresses (depth up to 1 μm) were measured using the multiple-reflection grazing incidence X-ray diffraction method with classical characteristic X-rays, while the deeper volumes (depth up to 10 μm) were investigated using energy-dispersive diffraction with white high energy synchrotron beam. Both complementary methods allowed for determining in-depth stress profile and the evolution of stress-free lattice parameter. It was confirmed that the crystals of tungsten are elastically isotropic, which simplifies the stress analysis and makes tungsten a suitable material for testing stress measurement methods. Furthermore, it was found that an important compressive stress of about − 1000 MPa was generated on the surface of the mechanically polished sample, and this stress decreases to zero value at the depth of about 9 μm. On the other hand, the strain-free lattice parameter does not change significantly in the examined subsurface region.

Neutron diffraction measurements of weld residual stresses in three-pass slot weld (Alloy 600/82) and assessment of the measurement uncertainty

This paper describes in detail two neutron diffraction residual stress measurements, performed on the ENGIN-X neutron scattering instrument at the ISIS facility in the UK and on the SALSA instrument at the Institut Laue-Langevin in Grenoble, France. The measurements were conducted as part of the NeT Task Group 6 (TG6) international measurement round robin on an Alloy 600/82 multi-pass weldment - a slot in an Alloy 600 plate filled with three Alloy 82 weld beads, simulating a repair weld. This alloy/weld combination is considered challenging to measure, due to the large grain size and texture in the weld, and large gradients in the stress-free lattice parameter between the parent and weld metal. The basic principles of the neutron diffraction technique are introduced and issues affecting the reliability of residual stress characterization are highlighted. Two different analysis strategies are used for estimation of residual stresses from the raw data. Chemical composition studies are used to measure the mixing of parent and weld metal and highlight the steep lattice parameter gradients that arise as a consequence. The inferred residual stresses are then compared with three sets of measurements performed on the same plate by other NeT partners on E3 at the HZB in Berlin, STRESS-SPEC at the FRM II in Munich and KOWARI in Sydney. A robust Bayesian estimation average is calculated from the combined five-instrument data set, allowing reliable best estimates of the residual stress distribution in the vicinity of the weldment. The systematic uncertainties associated with the residual stress measurements are determined separately in the weld and parent materials, and compared with those in the NeT TG4 benchmark. This is a three-pass slot-welded plate fabricated from American Iron and Steel Institute AISI 316L(N) austenitic stainless steel, and is normally considered less challenging to measure using diffraction techniques than all nickel welds. The uncertainties in the stress measurements by neutron diffraction for these two weldments seem to be comparable.

Determination of Internal Stresses During Pearlite Transformation of 0.8c–1.5Mn Steel Through <i>In-Situ</i> Neutron Diffraction

In this study, in-situ neutron diffraction during pearlite transformation and isothermal holding at 873 K after cooling of a 0.8C–1.5Mn steel specimen from 1323 K were conducted to measure the transformation stresses related to a eutectoid transformation. The stress relaxation behavior in cementite was also monitored to elucidate the relaxation of transformation elastic strains during isothermal annealing after pearlite transformation. By referring to the stress-free lattice parameter of an extracted electrolytic single-phase cementite sample after the long-time isothermal holding at 873 K, the transformation stresses were successfully evaluated. As one of the main findings, the elastic volume strain in cementite was determined to be approximately − 0.362%.

Multireflection grazing-incidence X-ray diffraction: a new approach to experimental data analysis

The multireflection grazing-incidence X-ray diffraction method is used to test surface stresses at depths of several micrometres in the case of metal samples. This work presents new ways of analysing experimental data obtained by this method for Ni samples exhibiting significant elastic anisotropy of crystals. Three different methods of determining biaxial stresses and lattice parameter were compared. In the first approach, the calculations were performed using the linear least-squares method, and then two simplified procedures based on simple linear regression (weighted and non-weighted) were applied. It was found that all the tested methods give similar results, i.e. almost equal values of the determined stresses and lattice parameters and the uncertainties of their determination. The advantage of analyses based on simple linear regression is their simplicity and straightforward interpretation, enabling easy verification of the influence of the crystallographic texture and the presence of shear stresses, as well as graphical determination of the stress-free lattice parameter.

Determining intrinsic stress and strain state of fibre-textured thin films by X-ray diffraction measurements using combined asymmetrical and Bragg-Brentano configurations

Measuring intrinsic macro stresses in fibre-textured thin films have always been challenging. Due to the nature of preferential orientation in these films, only d-spacings aligned with the film surface are observable in Bragg-Brentano X-ray diffraction scans, and to collect sufficient diffraction data needed for the stress calculation, a sample stage with tilt capabilities is essentially required. In this article, a new method is developed to lift this requirement. Based on the thin film crystal structure, an incident angle for asymmetrical XRD configuration is calculated to reveal tilted planes belonging to the same group of crystallites which are the textured majority. Measurement of d-spacing for this angle of incidence in combination with the Bragg-Brentano configuration is shown to successfully extract stress-free lattice parameter and the internal stress of the cubic metallic thin film. This method can also be adapted to determine stress and strain in polycrystalline thin films.

Competition between local lattice strains and distribution of metallic species in Ti1−xAlxN coatings with fluctuating [Ti]/[Al] ratio

The effect of a locally fluctuating [Ti]/[Al] ratio in the Ti1−xAlxN coatings on the formation of the lattice strains at the (Ti,Al)N/(Al,Ti)N interfaces and the influence of these interfaces on the stabilization of metastable (Al,Ti)N with face centered cubic structure were investigated using glancing angle X-ray diffraction, transmission electron microscopy and X-ray spectroscopy. A series of Ti1−xAlxN coatings with different [Ti]/[Al] ratios was deposited using cathodic arc evaporation from a titanium and an aluminum cathode. The overall chemical composition was controlled by the position of the respective sample in the deposition chamber and ranged from x = [Al]/([Ti] + [Al]) = 0.06 to 0.64. The local fluctuations of the [Ti]/[Al] ratio were produced by interrupting the deposition from the titanium cathode. It was shown that such local fluctuations of the [Ti]/[Al] ratio generate large contrary residual stresses at the respective side of the (Ti,Al)N/(Al,Ti)N interface. These stresses were almost completely relieved after annealing at 750 °C. The stress relaxation after annealing was accompanied by an equalization of the [Ti]/[Al] ratio and by a decay of the composition fluctuations in the Ti1−xAlxN coatings. The stress relaxation and the reduction of the local composition gradients were concluded from measured residual stresses, stress-free lattice parameters and local concentration profiles.

Structural and mechanical properties of NbN and Nb-Si-N films: Experiment and molecular dynamics simulations

The structural and mechanical properties of NbN and Nb-Si-N films have been investigated both experimentally and theoretically, in their as-deposited and annealed states. The films were deposited using magnetron sputtering at substrate bias (UB) between 0 and −70V. While NbN films were found to crystallize in the cubic δ-NbN structure, Nb-Si-N films with Si content of 11–13at% consisted of a two-phases nanocomposite structure where δ-NbN nanocrystals were embedded in SiNx amorphous matrix. Films deposited at UB=0V were highly (001)-textured. Application of substrate bias potential led to a depletion of light atoms, and caused a grain size refinement concomitantly with the increase of (111) preferred orientations in both films. The maximum hardness was 28GPa and 32GPa for NbN and Nb-Si-N films, respectively. NbN and Nb-Si-N films deposited at UB=−70V exhibited compressive stress of −3 and −4GPa, respectively. After vacuum annealing, a decrease in the stress-free lattice parameter was observed for both films, and attributed to alteration of film composition. To obtain insights on interface properties and related mechanical and thermal stability of Nb-Si-N nanocomposite films, first principles molecular dynamics simulations of NbN/SiNx heterostructures with different structures (cubic and hexagonal) and atomic configurations were carried out. All the hexagonal heterostructures were found to be dynamically stable and weakly dependent on temperature. Calculation of the tensile strain-stress curves showed that the values of ideal tensile strength for the δ-NbN(111)- and ε-NbN(001)-based heterostructures with coherent interfaces and Si3N4–like Si2N3 interfaces were the highest with values in the range 36–65GPa, but lower than corresponding values of bulk NbN compound. This suggests that hardness enhancement is likely due to inhibition of dislocation glide at the grain boundary rather than interfacial strengthening due to Si-N chemical bonding.

Structural and mechanical properties of Nb1 − xTixN thin films deposited by rf magnetron sputtering

Nb1−xTixNy thin films with different nitrogen contents (0.5<y<1.2) and Nb/Ti ratios (0≤x≤1) were investigated because of their potential to improve the lifetime of bearing components of orthopaedic implants. The films were deposited onto a medical-grade CoCrMo substrate by rf magnetron sputtering at 400°C under a (N2+Ar) atmosphere. The samples were characterised using Rutherford backscattering spectroscopy (RBS), elastic recoil detection analysis (ERDA), X-ray diffraction (XRD) at grazing incidence and Bragg–Brentano geometry, scanning and transmission electron microscopy (SEM, TEM), and nanoindentation to investigate the dependence of the phase configuration, microstructure, and mechanical behaviour on the nitrogen content and Nb/Ti ratio. The results demonstrated that the coatings develop mixed structures composed of fcc-cubic as the major phase and hexagonal (β, ε, and δ′) phases as the minor constituents. The formation of hexagonal phases is nitrogen-dependent: (β, ε) for N2/(N2+Ar)<20%, and (δ′) for ratios >40%. The cubic and hexagonal phases simultaneously grow during the nucleation and early stage of growth up to a thickness of approximately 0.6μm, but the hexagonal phase gradually decreases through the film thickness, thereby giving rise to single-phase deposits at the upper part of the coatings. The addition of Ti improved the crystallinity and favoured the formation of the cubic phase, whereas a solid solution fcc δ-Nb1−xTixN was observed for the entire range of (x). The dominant orientation of the crystallites was (111), while a significant contribution of (311) was detected at higher Nb/Ti. The determination of stressed and stress-free lattice parameters allowed correlating the relative reduction of the compressive residual stress, hardness, and modulus in the nitrogen-rich films to the formation of vacancies in the metal sublattice.

Effect of oxygen incorporation on the structure and elasticity of Ti-Al-O-N coatings synthesized by cathodic arc and high power pulsed magnetron sputtering

Ti-Al-O-N coatings were synthesized by cathodic arc and high power pulsed magnetron sputtering. The chemical composition of the coatings was determined by means of elastic recoil detection analysis and energy dispersive X-ray spectroscopy. The effect of oxygen incorporation on the stress-free lattice parameters and Young's moduli of Ti-Al-O-N coatings was investigated by X-ray diffraction and nanoindentation, respectively. As nitrogen is substituted by oxygen, implications for the charge balance may be expected. A reduction in equilibrium volume with increasing O concentration is identified by X-ray diffraction and density functional theory calculations of Ti-Al-O-N supercells reveal the concomitant formation of metal vacancies. Hence, the oxygen incorporation-induced formation of metal vacancies enables charge balancing. Furthermore, nanoindentation experiments reveal a decrease in elastic modulus with increasing O concentration. Based on ab initio data, two causes can be identified for this: First, the metal vacancy-induced reduction in elasticity; and second, the formation of, compared to the corresponding metal nitride bonds, relatively weak Ti-O and Al-O bonds.

Structural effects of energy input during growth of Ti1 − xAlxN (0.55 ≤ x ≤ 0.66) coatings by cathodic arc evaporation

Effects of growth conditions on structural properties are investigated for the case of Ti1−xAlxN (0.55≤x≤0.66) deposition by cathodic arc evaporation. The evolution of residual stress, stress free lattice parameter, crystalline content, grain size, growth rate, and ion irradiation is studied as functions of the following parameters: Al content, process temperature, substrate bias potential, arc current, and magnetic field in front of the cathode.The evolution of residual stress is explained in terms of generation and annihilation of defects. Generation of defects, as indicated by increased compressive stress and stress free lattice parameter, is found to be directly connected to an increased ion energy caused by either higher bias potential or increased (estimated) average charge state of the depositing species. Annihilation of defects, indicated by decreased compressive stress and stress free lattice parameter, is observed as process temperature or arc current is raised, where the effect of arc current becomes stronger at higher magnetic field strength. It is concluded that the most likely explanation is thermal activation caused, directly or indirectly, by the applied process parameters.The results also show a strong decrease in grain size as either of the studied parameters is increased. The grain refinement is found to be correlated to an increase in the amount of wurtzite phase, in addition to the majority NaCl phase, as detected by X-ray diffraction. It is proposed that the probability of forming wurtzite becomes higher as either the energy available increases (due to thermal activation) or the energetic difference between the two phases becomes smaller (e.g., as the Al content is increased from x=0.55 to x=0.66). This explanation is consistent with the evolution of grain size and phase content as functions of process conditions or Al content, and is further supported by the results on residual stress evolution.

Atom insertion into grain boundaries and stress generation in physically vapor deposited films

We present evidence for compressive stress generation via atom insertion into grain boundaries in polycrystalline Mo thin films deposited using energetic vapor fluxes (&amp;lt;∼120 eV). Intrinsic stress magnitudes between −3 and +0.2 GPa are obtained with a nearly constant stress-free lattice parameter marginally larger (0.12%) than that of bulk Mo. This, together with a correlation between large compressive film stresses and high film densities, implies that the compressive stress is not caused by defect creation in the grains but by grain boundary densification. Two mechanisms for diffusion of atoms into grain boundaries and grain boundary densification are suggested.

Structure-stress-resistivity relationship in WTi alloy ultra-thin and thin films prepared by magnetron sputtering

WTi thin films were prepared from an alloyed target (W:Ti ∼ 70:30 at. %) by magnetron sputtering. Body-centered cubic WxTi1−x solid solutions with a {110} fiber texture and columnar grains have been produced with 0.75&amp;lt;x&amp;lt;0.81. The sub-stoichiometry of Ti is shown to result from atom transport and, to a lesser extent, from resputtering. The stress-free lattice parameter values of the films are shown to be close to the bulk lattice parameter of α-W. The electrical resistivity of the produced WTi thin films is about 60−200 μΩ cm, depending on the film thickness and microstructure (sputtering conditions). For both ultra-thin (9.5 nm) and thin (180 nm) films, a stress transition from compressive to tensile is observed as the working pressure increases. The process-structure-property relations of the WTi ultra-thin and thin films are discussed in relation with the state of the art.

Effect of bias voltage on microstructure and mechanical properties of arc evaporated (Ti, Al)N hard coatings

In the present study, authors report on the effect that substrate bias voltage has on the microstructure and mechanical properties of (Ti, Al)N hard coatings deposited with cathodic arc evaporation (CAE) technique. The coatings were deposited from a Ti 0· 5Al 0· 5 powder metallurgical target in a reactive nitrogen atmosphere at three different bias voltages: U B = − 25, −50 and −100 V. The coatings were characterized in terms of compositional, microstructural and mechanical properties. Microstructure of the coatings was investigated with the aid of X-ray diffraction in glancing angle mode, which revealed information on phase composition, crystallite size, stress-free lattice parameter and residual stress. Mechanical properties were deduced from nano-indentation measurements. The residual stress in all the coatings was compressive and increased with increasing bias voltage in a manner similar to that reported in literature for Ti–Al–N coatings deposited with CAE. The bias voltage was also found to significantly influence the phase composition and crystallite size. At −25 V bias voltage the coating was found in single phase fcc-(Ti, Al)N and with relatively large crystallites of ~ 9 nm. At higher bias voltages (−50 and −100 V), the coatings were found in dual phase fcc-(Ti, Al)N and fcc-AlN and the size of crystallites reduced to approximately 5 nm. The reduction of crystallite size and the increase of compressive residual stress with increasing bias voltage both contributed to an increase in hardness of the coatings.

Effect of the deposition process and substrate temperature on the microstructure defects and electrical conductivity of molybdenum thin films

The effect of point defects, dislocations and grain boundaries on the electron scattering in molybdenum thin films having a constant thickness of 500nm was described quantitatively in form of a dependence of the electrical resistivity on the concentration of impurity atoms, stress-free lattice parameter, microstrain and grain size. The concentration of impurity atoms and the dislocation density were modified by depositing the Mo thin films using different techniques (DC magnetron sputtering, pulsed DC magnetron sputtering and RF magnetron sputtering) and by varying the substrate temperature (25°C, 150°C, 250°C and 350°C). As expected, the electrical resistivity of the Mo films decreased with decreasing density of microstructure defects. For all deposition methods, the dislocation density decreased with increasing substrate temperature, which led to an overall decrease of the measured resistivity with increasing substrate temperature. Due to the deposition equipment constraints during the RF sputtering, up to 3at.% of Fe, Cr and Ni were incorporated at the regular lattice positions in the crystal structure of molybdenum, which increased the resistivity of the Mo films nearly two times as compared to the DC and pulsed DC sputtered films.

Structural and elastic properties of ternary metal nitrides TixTa1 − xN alloys: First-principles calculations versus experiments

First-principles pseudopotential calculations of the lattice constants and of the single-crystal elastic constants for TixTa1−xN (0≤x≤1) alloys with B1-rocksalt structure were first carried out. These calculations were performed using density functional perturbation theory (DFPT) within the virtual crystal approximation (VCA) for the disordered alloys and the supercell method (SC) for the ordered alloys, with the ABINIT program. For disordered structures, partial comparisons of the lattice constants and of the bulk modulus are provided with calculations that used the coherent potential approximation (CPA) with the exact muffin-tin orbitals (EMTO). For the exchange-correlation potential we used the generalized gradient methods (GGA). The calculated equilibrium lattice parameters by VCA are in good agreement with the stress-free lattice parameters a0 and exhibit a positive deviation from Vegard's rule corresponding to a positive bowing parameter while the calculated single-crystal stiffness c12 and c44, gradually increase when c11 decreases from TaN to TiN. In a second stage, we have estimated by homogenization methods the averaged stiffnesses <cij>, the Young modulus and Poisson ratio of polycrystalline TixTa1−xN (0≤x≤1) alloys considering a random orientation of crystallites. Finally, comparisons are made with the experimental effective out-of-plane shear elastic modulus C44 and the effective out-of-plane longitudinal elastic constant C33 measured by Brillouin light scattering and picosecond ultrasonics, respectively, on thin films elaborated by magnetron sputtering.

Structure, phase stability and elastic properties in the Ti1–xZrxN thin-film system: Experimental and computational studies

The composition-dependence of the structure and elastic properties of ternary Ti1–xZrxN alloys is systematically investigated by combining thin film growth and ab initio calculations. Single-phase Ti1–xZrxN thin films (0⩽x⩽1) with a rocksalt structure have been deposited using dc reactive magnetron sputtering at Ts=300°C in Ar/N2 plasma discharges. The structure, stress state and phase stability upon thermal annealing were studied by X-ray diffraction (XRD), while the acoustic and elastic properties were measured using Brillouin light spectroscopy, picosecond ultrasonics and nanoindentation. First-principles pseudopotential calculations of the total energy, lattice constants, bulk modulus, and single-crystal elastic constants Cij for several cubic ordered structures of Ti1–xZrxN alloys were also carried out. The positive values of the computed formation energies indicate that the homogeneous Ti1–xZrxN alloys can be only stabilized at high temperatures. However, the magnetron-sputtered thin films were found to retain their as-grown single-phase cubic structure during post-deposition annealing at 850°C for 3h. The calculated equilibrium lattice parameters are in good agreement with the stress-free lattice parameters a0 determined experimentally from XRD using the sin2ψ method: they both exhibit a positive deviation from Vegard-like linear interpolation. The calculated bulk modulus, elastic constants and Poisson’s ratio gradually decrease from TiN to ZrN. These computed values were used to interpret the experimentally derived elastic constants and Young’s modulus as functions of composition.

Structure and Mechanical Properties of AlCrN Thin Films Deposited by Magnetron Sputtering

A magnetron sputtering system was used to deposit AlCrN thin films. Chemical compositions of the films were determined by both EDXS and RBS, while structures analyses were conducted by XRD in a Seifert XRD3000 diffractometer. Macroscopic residual stresses of films were determined by curvature measurements using DEKTAK IIA profilometer, while in-grain stresses were extracted by the “sin²Y method” from XRD measurements. A nanoindenter from CSM (Switzerland) was used to determine the hardness of the films. A CrN type FCC structure was obtained with a strong (200) fiber texture for the range of compositions Al1-xCrxNy(0.56 &lt; x&lt; 0.89) of interest here. The global stresses were compressive for all FCC films resulting from the high energetic deposition conditions used. In-grain compressive stresses were determined for the films with thickness &lt; 500nm, while thicker films (&gt; 500nm) showed tensile in-grain stresses. Stress-free lattice parameter a0strongly decreased from 4.13 to 3.97 A°. Hardness values were obtained in a range extending from 17 to 27 GPa with an increase obtained as Cr content increases and correlated to the residual-stress level.