Hardness Mapping Research Articles

The studies on the tribological performance, characterization and mechanical properties of W-2Ni-1Fe (wt%) alloy

Friction, wear and mechanical properties of the liquid phase sintered W-2Ni-1Fe (wt%) alloy were investigated. Tribological tests were carried out at different loads, frequencies and sliding distances under reciprocative sliding condition, against tungsten carbide (WC-Co) counter body. Co-efficient of friction (COF), wear volume and specific wear rate were determined. The dominant operative wear mechanisms were identified in different testing conditions. Abrasive wear and tribo-chemical wear mechanisms were found to be the dominant wear mechanisms. Room temperature strain rate sensitivity was determined by conducting jump test in tensile mode. The alloy showed low strain rate sensitivity with significant strain hardening. High resolution nanoindention mapping was carried out to establish structure property correlations at the micro-meter length scale. The hardness and elastic modulus maps were generated to determine the hardness and elastic modulus of the constituent phases of W and of γ-Ni matrix. The maps were found to correlate well with the actual microstructure obtained from opticaland electron microscopy.

The Effect of Temper Condition and Feeding Speed on the Additive Manufacturing of AA2011 Parts Using Friction Stir Deposition.

In the current study, solid-state additive manufacturing (SSAM) of two temper conditions AA2011 was successfully conducted using the friction stir deposition (FSD) process. The AA2011-T6 and AA2011-O consumable bars of 20 mm diameter were used as a feeding material against AA5083 substrate. The effect of the rotation rate and feeding speed of the consumable bars on the macrostructure, microstructure, and hardness of the friction stir deposited (FSD) materials were examined. The AA2011-T6 bars were deposited at a constant rotation rate of 1200 rpm and different feeding speeds of 3, 6, and 9 mm/min, whereas the AA2011-O bars were deposited at a constant rotation rate of 200 mm/min and varied feeding speeds of 1, 2, and 3 mm/min. The obtained microstructure was investigated using an optical microscope and scanning electron microscope equipped with EDS analysis to evaluate microstructural features. Hardness was also assessed as average values and maps. The results showed that this new technique succeeded in producing sound additive manufactured parts at all the applied processing parameters. The microstructures of the additive manufactured parts showed equiaxed refined grains compared to the coarse grain of the starting materials. The detected intermetallics in AA2011 alloy are mainly Al2Cu and Al7Cu2Fe. The improvement in hardness of AA2011-O AMPs reached 163% of the starting material hardness at the applied feeding speed of 1 mm/min. The hardness mapping analysis reveals a homogeneous hardness profile along the building direction. Finally, it can be said that the temper conditions of the starting AA2011 materials govern the selection of the processing parameters in terms of rotation rate and feeding speed and affects the properties of the produced additive manufactured parts in terms of hardness and microstructural features.

A guide to synchrotron hard X-ray fluorescence mapping of annually laminated stalagmites: Sample preparation, analysis and evaluation

Annually laminated stalagmites are an exceptional archive of high-resolution past hydroclimate changes and provide robust annually-resolved age models. Stalagmite chemical annual laminae are invisible through optical and fluorescence microscopy, but are revealed by X-ray fluorescence or mass-spectrometry techniques. Synchrotron radiation based micro-X-ray fluorescence (S-μXRF) has the unique advantage of creating 2-dimensional maps of element distribution, which allows visualizing lateral heterogeneity and porosity that pose problems when one dimensional line-scanning techniques, such as LA-ICP-MS, are used. Here, we show how S-μXRF fast element mapping allows obtaining robust age models and palaeoclimate data from stalagmites otherwise difficult to date. Analytical challenges and solution to problems are discussed for both thick polished slabs and thin sections. The elements detectable through the fast acquisition mode (dwell time 1 to 4 ms) are typically Ca, Sr, Br, while Fe, Zn, Ni, Cu, Mn, Y, and Rb are occasionally detected in few distinctive layers or, in association with grain inclusions and porosity. Only Sr, however, exhibits a consistent and clear annual cyclicity. At incident angles of 90° the attenuation depth for Sr is ca. 240 μm and, therefore thick samples are preferable as they produce stronger fluorescence signal and sharper images unaffected by non-linear drift. On the other hand, thick samples are more affected by geometric and edge effects that can be particularly severe in the presence of irregular lamination and when the laminae are dipping with variable angle within the sample. The Sr concentration in the tropical stalagmites analysed in this study varied from 15 to 600 ppm, which strongly influences the dwell time needed to obtain high-quality maps. For Sr concentration below 20 ppm the ideal dwell time exceeds 20 ms and this renders the acquisition of large maps (> 20 Megapixels) hardly feasible. For concentrations above 20 ppm the fast mapping (dwell time < 5 ms) through S-μXRF is by far the best methodology to visualise chemical annual cycles in stalagmites.

Analysis of residual plastic deformation of blanked sheets out of automotive aluminium alloys through hardness map

Reducing overall vehicle weight is essential to reduce fuel consumption and pollutant emission and to improve noise, vibration, and harshness (NVH) performances. The substitution with lighter alloys can involve the grand majority of vehicle components, depending on the market sector. In several applications, e.g., chassis, pulleys, and viscodampers, metal sheets are formed in several steps, each of whom work-hardens the material reducing the available residual plasticity. Typically, the process is designed via FEM, whose results are affected by the initial conditions, often neglected, and is performed on pre-processed materials from suppliers. In this regard, correctly simulating the first step of the process is critical. However, the related initial conditions, in terms of residual stress and strain induced by former preliminary operations, are often neglected. This work proposes a quick and economical experimental procedure based on a hardness map to estimate initial conditions and to validate FEM results. The procedure allows evaluating the material’s residual plasticity, which is necessary to process engineers to design following manufacturing steps. The approach is demonstrated on an industrially relevant case study, i.e., the blanking of an AA 5754, in use for water pump pulleys.

Effect of laser heat treatments on the hardness of tool steels

The application of laser heat treatments (LHT) has been growing attention in the last years, due to the effectiveness of localized hardening that can improve the tribological properties of steels. AISI P20 mod. steel is commonly used for plastic injection moulds applications and can be heat-treated to achieve high hardness values. This work presents an experimental investigation on the laser local heat treatments effect on the hardness of AISI P20 mod. steel parts, using a high-power diode laser. Different heat treatments at 1060 °C and 1100 °C using a feed rate of 10 mm·s-1 and 15 mm·s-1 were applied on the steel. The LHT were assessed through the hardness mapping trough depth and width. The results showed that the hardness of as-received P20 mod. tool steel is approximately 300 HV, and after LHT occurred an increment to around 625 HV with a fair hardness distribution. LHT had a minimum of 0.8mm and a maximum of 1.0mm depth.

Inconel 625/AISI 413 Stainless Steel Functionally Graded Material Produced by Direct Laser Deposition.

Functionally graded material (FGM) based on Inconel 625 and AISI 431 stainless steel powders was produced by applying the direct laser deposition (DLD) process. The FGM starts with layers of Inconel 625 and ends with layers of 431 stainless steel having three intermediate zones with the composition (100-X)% Inconel 625-X% 431 stainless steel, X = 25, 50, and 75, in that order. This FGM was deposited on a 42CrMo4 steel substrate, with and without preheating. Microstructures of these FGMs were evaluated, while considering the distribution of chemical composition and grain structure. Microstructures mainly consisted of columnar grains independent of preheating condition; epitaxial growth was observed. The application of a non-preheated substrate caused the formation of planar grains in the vicinity of the substrate. In addition, hardness maps were produced. The hardness distribution across these FGMs confirmed a smooth transition between deposited layers; however, the heat-affected zone was greatly influenced by the preheating condition. This study suggests that an optimum Inconel 625/AISI 431 FGM obtained by DLD should not exceed 50% AISI 431 stainless steel.

Cryogenic temperature equal channel angular pressing of pure titanium: microstructure and homogeneity

Samples of pure titanium with a purity of 99.99 wt.% were successfully processed by equal channel angular pressing (ECAP) at cryogenic temperature. Deformed microstructures of ECAPed samples were characterized by electron backscattering diffraction (EBSD), and its homogeneity was studied by color-coded contour mapping of microhardness distribution. EBSD results indicate the original coarse grains with an average grain size of 196 μm were significantly refined to 0.56 μm after four passes, and that the prism <a> slip systems were activated in the whole deformation process and with increasing passes number more slip systems were activated. The hardness mapping reveals that the microstructure of samples prior to ECAP is basically homogeneous but becomes inhomogeneous after one pass and then gradually homogeneous with additional passes. In addition, the grain refinement of ECAPed titanium at cryogenic temperature was discussed and confirmed by CDRX. Also, the factors of influence on the homogeneity of microstructure were analyzed.

High-speed wide-angle interleaved scanning technique for a 3D imaging lidar

In this paper, we describe a novel interleaved scanner for an eye-safe 3D scanning lidar system to measure aerodynamic phenomena in a wind tunnel using elastic backscatter from seeding particles. The scanner assembly consists of a rotating polygon scanner for line scanning along the fast axis, a galvanometer (galvo) scanner for scanning along the slow axis, angular position sensors, and motor controllers. The polygon scanner sweeps the lidar beam at up to 10,000 lines/s across a 27 deg angular field of regard in the fast axis, while the galvo scanner covers an angular range of 20 deg in the slow axis. Using this scanner, the lidar can perform nonintrusive flow visualization, velocimetry, and hard target mapping at millimeter-scale spatial resolution to a standoff range of 5 m at an update rate of 50 Hz for the full field of regard. An interleaved scanning methodology for the acquisition of two snapshots of 3D lidar intensity data with a 100 µs time offset is discussed. The design of the control and data acquisition electronics is described. The effects of rapid scanning on the response of a narrow field-of-view lidar are addressed. The design of the scanner is scalable and can be tailored to meet the requirements of other applications by increasing or decreasing the standoff range, angular field of regard, and scan rate.

Evaluation of ductile fracture in welded tubes with tensile, hardness, flaring tests

A continuum damage model (CDM) based on local hardness in welds is developed to predict fracture of welded tubes. A regression function of hardness distribution in the welds is proposed to establish hardness continuously through hardness mapping method in the finite element model. A constitutive model of the weld zone is determined by the rule of mixture, which estimates the flow stress of the welds from the hardness ratio. Coefficients of the flow stress model in the welds are validated by comparing finite element analysis (FEA) solution and experimental load - displacement data of tensile specimens. Softening after necking is considered by Lemaitre CDM. A damage parameter is newly given as a function of hardness ratio varying with angular position. Coefficients of damage parameter are obtained by the inverse FEA of tensile and flaring tests. The proposed method finely predicts the ductile fracture of welded tubes by considering local plastic properties and damage evolution.

Development of microstructure and residual stress in electron beam welds in low alloy pressure vessel steels

Reduced-pressure electron beam (EB) plate butt welds were manufactured in two low-alloy pressure-vessel steels, SA508 Gr 3 Cl 1 and SA508 Gr 2, at two thicknesses in both steels, 30 mm and 130 mm. Transient temperatures during welding were recorded using thermocouple arrays. Residual stresses in the as-welded condition and after post-weld heat treatment were measured using diverse methods: neutron diffraction and the contour method at 30 mm thickness; and deep hole drilling and the contour method at 130 mm. Incremental centre hole drilling measurements were performed at 130 mm thickness to better understand near-surface stresses. Weld and heat-affected zone microstructures and microconstituents were evaluated using a combination of hardness mapping, optical microscopy and electron microscopy. The as-welded residual stresses exhibit the characteristic M-shaped distribution for hardenable steels, reaching 500–600 MPa in tension in both steels at both thicknesses. However, the modest changes to the chemical composition and the change in plate thickness both significantly influenced microstructures, mechanical properties and residual stress distributions. These sensitivities underline the need for physically faithful models. This extensive characterisation study enables the development and validation of models that predict the development of microstructures and residual stresses in EB welds in low alloy pressure vessel steels.

The Effect of Bad Heat Treatment Technology on Failure Mode of Armor Steel Sheet under EN1522 Ballistic Test

Armor steel is a special grade of steel that is commonly designed for providing protection of the army resources from different piercing ammunitions. This steel must be assessed through its mechanical properties, and its ballistic resistant to confirm their ability to withstand the resistance of armor-piercing ammunition, before being subjected to use. Case study of armor steel sheet 6mm thickness that has been subjected for normal ballistic test EN1522, one projectile passed through the sheet, while the other two projectiles have fired at the surface of the sheet. Then, this research was designed to investigate the root cause of failure of this armor steel sheet 6mm under ordinary ballistic test. Constituent structures of steel have been monitored and estimated by using Optical, Scanning electron microscope, Micro hardness tester, and X-ray diffractometer. In addition, hardness map at the surface of the investigated sheet has been detected. Finally, thermal transformation of this steel has been determined by using Dilatometer. The results refer that the root cause of failure should be attributed to the inhomogeneity in the microstructure among the sheet area, which certainly refers to the poor homogeneity at the heat treatment cycle used at the production site.

Microstructural evolution of P92 steel in IN740H/P92 dissimilar weld joints during creep deformation

In this study, we report the microstructural development of heat-affected zone in P92 heat-resistant steel during creep deformation in cross-weld specimens with dissimilar weld joints between IN740H/P92 materials. Different specimens were prepared via the interruption of creep testing at 50, 70, and 90% of the measured creep-rupture life and were carefully examined and compared. To explain the deformation behavior, finite element analysis was performed in conjunction with softening behavior measured by electron back-scattered diffraction and hardness mapping. The FGHAZ II region defined in this study could be related to the generally known inter-critical heat-affected zone, which showed major changes in microstructure during creep deformation due to the accelerated softening by dynamic recrystallization as well as to the development of a triaxial stress state. As a result, cavity formation and growth was observed only in the FGHAZ II region, which ultimately led to fracture.

Genome-wide association analysis permits characterization of\xa0Stagonospora nodorum blotch (SNB) resistance in hard winter wheat

Stagonospora nodorum blotch (SNB) is an economically important wheat disease caused by the necrotrophic fungus Parastagonospora nodorum. SNB resistance in wheat is controlled by several quantitative trait loci (QTLs). Thus, identifying novel resistance/susceptibility QTLs is crucial for continuous improvement of the SNB resistance. Here, the hard winter wheat association mapping panel (HWWAMP) comprising accessions from breeding programs in the Great Plains region of the US, was evaluated for SNB resistance and necrotrophic effectors (NEs) sensitivity at the seedling stage. A genome-wide association study (GWAS) was performed to identify single‐nucleotide polymorphism (SNP) markers associated with SNB resistance and effectors sensitivity. We found seven significant associations for SNB resistance/susceptibility distributed over chromosomes 1B, 2AL, 2DS, 4AL, 5BL, 6BS, and 7AL. Two new QTLs for SNB resistance/susceptibility at the seedling stage were identified on chromosomes 6BS and 7AL, whereas five QTLs previously reported in diverse germplasms were validated. Allele stacking analysis at seven QTLs explained the additive and complex nature of SNB resistance. We identified accessions (‘Pioneer-2180’ and ‘Shocker’) with favorable alleles at five of the seven identified loci, exhibiting a high level of resistance against SNB. Further, GWAS for sensitivity to NEs uncovered significant associations for SnToxA and SnTox3, co-locating with previously identified host sensitivity genes (Tsn1 and Snn3). Candidate region analysis for SNB resistance revealed 35 genes of putative interest with plant defense response-related functions. The QTLs identified and validated in this study could be easily employed in breeding programs using the associated markers to enhance the SNB resistance in hard winter wheat.

Diffusion Bonding of Ti6Al4V to Al2O3 Using Ni/Ti Reactive Multilayers

This paper aims to investigate the diffusion bonding of Ti6Al4V to Al2O3. The potential of the use of reactive nanolayered thin films will also be investigated. For this purpose, Ni/Ti multilayer thin films with a 50 nm modulation period were deposited by magnetron sputtering onto the base materials. Diffusion bonding experiments were performed at 800 °C, under 50 MPa and a dwell time of 60 min, with and without interlayers. Microstructural characterization of the interface was conducted through scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS). The joints experiments without interlayer were unsuccessful. The interface is characterized by the presence of a crack close to the Al2O3 base material. The results revealed that the Ni/Ti reactive multilayers improved the diffusion bonding process, allowing for sound joints to be obtained at 800 °C for 60 min. The interface produced is characterized by a thin thickness and is mainly composed of NiTi and NiTi2 reaction layers. Mechanical characterization of the joint was assessed by hardness and reduced Young’s modulus distribution maps that enhance the different phases composing the interface. The hardness maps showed that the interface exhibits a hardness distribution similar to the Al2O3, which can be advantageous to the mechanical behavior of the joints.

The Effects of HLAW Parameters for One Side T-Joints in 15 mm Thickness Naval Steel

The present contribution is the first research reporting full penetration HLAW joints in 15 mm thick EH36 steel butt T-welds with square grooves on 2F welding position by single-sided welding. The effects of welding parameters were investigated to increase the quality of the joints. Conditions leading to defect-free full penetration welds fulfilling naval regulations includes a laser power of 12.5 kW, a welding speed of 1.6 m/min and the vertical laser offset distance from the flange of 1 mm. Advanced characterization of selected welds included a microstructural identification by optical microscopy, SEM, and XRD, revealing the presence of acicular, polygonal and Widmanstätten ferrite, lath martensite, and some retained austenite at FZ. Hardness and microhardness mapping tests showed values of 155 HV at base metal and 200 to 380 HV at the fusion zone connecting the web to the flange.

Improving the mechanical performance of a resistance spot welded 1200 MPa TBF steel

Abstract In the present work different approaches to improve the mechanical properties of a resistance spot welded 1200 MPa transformation induced plasticity-aided bainitic ferrite steel are evaluated. An extension of the welding time results in coarsening of the microstructure of the outer fusion zone and the maximum force derived by the cross tension strength test did not improve significantly. A temper pulse after a long cooling time leads to pronounced softening of the fusion zone, as determined by hardness mapping, which resulted in enhanced weld properties. A recrystallization pulse modifies the shape of the prior austenite grains at the outer fusion zone, which was visualized with electron backscatter diffraction. This also resulted in a significant improvement of maximum force. For all approaches the failure mode improved, which can be attributed to an increased fraction of high angle grain boundaries at the edge of the fusion zone.

Revealing the relation between microstructural heterogeneities and local mechanical properties of complex-phase steel by correlative electron microscopy and nanoindentation characterization

Compositional and microstructural heterogeneity are characteristics of modern multiphase steels. However, the quantitative characterization of these heterogeneities is rarely considered in scientific publications. We characterized the compositional and microstructural heterogeneity of a commercial complex-phase steel (CP800) by combining various electron microscopy techniques and nanoindentation. Compositional gradients of C and Mn were characterized qualitatively and quantitatively through electron probe microanalysis (EPMA). Electron backscatter diffraction (EBSD) results were utilized to identify and segment the microstructural constituents. A novel nanoindentation approach was used to obtain hardness maps. Cube-corner indenter and micro-newton load were applied to limit the indent depth and spacing between adjacent indents to the nanometer scale. A high-resolution hardness map was obtained and successfully overlapped with EPMA and EBSD results, based on which the correlation between compositional heterogeneity and hardness variation in complex-phase microstructure was successfully established.

Welding thermal efficiency in cold wire gas metal arc welding

Cold wire gas metal arc welding (CW-GMAW) has been increasingly used in heavy-gauge manufacturing where high deposition rates are required. In such applications, the thermal efficiency of the CW-GMAW is crucial, yet it is not reported in the literature. Water calorimetry experiments were conducted to assess the thermal efficiency of CW-GMAW for two cold wire feed fractions and three common transfer modes: short circuit, globular, and spray, and these are compared to standard GMAW using the same transfer modes. The welds were produced using ER70S-6 as the electrode and cold wires. AISI 1020 plain carbon steel plates were used as the base metal with thicknesses of 9.53 mm and 6.35 mm. After producing the welds, three cross-sections were cut and analyzed using Vickers hardness maps, where differences were attributed to cooling variation rate across the weld cross-sections in high arc power samples. Results have shown that feeding a cold wire into the arc can re-introduce part of the lost heat back into the weld pool both in the short circuit and spray transfer regimes, suggesting an increase in the heat content in the weld pool.

Quantifying the effect of oxygen on micro-mechanical properties of a near-alpha titanium alloy

Titanium alloys are widely used in the aerospace industry, yet oxygen ingress can severely degrade the mechanical properties of titanium alloy components. Atom probe tomography (APT), electron probe microanalysis (EPMA) and nanoindentation were used to characterise the oxygen-rich layer on an in-service jet engine compressor disc, manufactured from the titanium alloy TIMETAL 834. Oxygen ingress was quantified and related to changes in mechanical properties through nanoindentation studies. The relationship between oxygen concentration, microstructure, crystal orientation and hardness has been explored through correlative hardness mapping, EPMA and electron backscatter diffraction (EBSD). It has been found that the hardening effects of microstructure and crystallography are only significant at very low-oxygen concentrations, whereas interstitial solid solution hardening dominates by order of magnitude for higher oxygen concentrations. The role of microstructure on oxygen ingress has been studied and oxygen ingress along a potential α/β interface was directly observed on the nanoscale using APT.

Mechanical properties and fracture modes of thin butt-joined aluminum-steel blanks for automotive applications

The influence of different filler alloys and joining parameters on the mechanical properties and on the fracture modes of aluminum-steel blanks for automotive applications was experimentally investigated. Sheets of 1.15-mm-thick aluminum alloy EN AW-6014 T4 were butt-joined with sheets of 0.80-mm-thick zinc-coated steel DC04 using the single-sided Cold Metal Transfer (CMT) process. The quasi-static strength and the fracture modes of the joints were determined using uniaxial tensile and three-point bending tests. The width of the heat-affected zone (HAZ) was estimated based on hardness profiles and maps. The microstructure inside the HAZ was studied using optical micrographs, and selected fracture surfaces were investigated by means of scanning electron microscopy (SEM). The influence of the filler alloy composition was more significant under tensile load than under bend load. Under tensile load three different fracture modes depending on the actual location of fracture were identified. The most brittle behavior of the joint was observed, if fracture occurred directly at the weld seam. Both, thickening of the intermetallic (IM) layer between the weld seam and the steel sheet as well as the porosity forming during the joining process, facilitated fracture at the weld seam. Most favourable combinations of strength and ductility under both tensile and bend loads were obtained when using comparatively silicon-rich filler alloys Al-3Si-1Mn or Al-1Si-Mg-Mn at the welding speed of 0.4 m/min. Increasing the welding speed to 0.7 m/min may still result in acceptable strength and ductility of the joints; however, further increase to 1.0 m/min reduces these properties considerably.