Ultrasonic Nanocrystal Surface Modification Research Articles

Advancement of tribological properties of Ti–6Al–4V alloy fabricated by selective laser melting

In this study, the influence of UNSM (ultrasonic nanocrystal surface modification) temperature on the tribological properties of Ti–6Al–4V alloy was investigated. The UNSM bore influence on the tribological properties, where the coefficient of friction (COF) of the as-SLM sample was reduced by about 25.8% and 305% and the wear resistance was enhanced by about 41% and 246% at RT and HT, respectively. These are essentially attributed to the enhanced strength, smoothed surface and expelled pores from the surface. Based on SEM images, the damage caused by abrasive wear was the most dominant in the wear track of the as-SLM sample. UNSM temperature-dependent wear mechanisms were comprehensively investigated and elaborated based on the obtained experimental data and observed microstructural images.

Optimization of ultrasonic nanocrystal surface modification for surface quality improvement of directed energy deposited stainless steel 316L

Ultrasonic nanocrystal surface modification (UNSM) technology can be used for the surface treatment of specimens produced by additive manufacturing using directed energy deposition. We investigated the change in the surface quality characteristics of the treated specimens with respect to the UNSM process variables. The roughness and waviness of the deposited surface were adopted as the objective functions and the optimal process conditions were determined by the response surface method (RSM). The surface waviness and roughness were determined to be most affected by the static load, with the scanning speed having the least effect. It was observed that a smaller inter-path interval decreased the surface waviness and roughness, and an excessively large or small static load deteriorated the surface modification results. The finally optimized conditions consisted of a static load of 45 N, inter-path interval of 10 μm, and scanning speed of 2600 mm/min. These conditions produced a surface waviness of 1.8097 μm and roughness of 0.3297 μm, which represent improvements of 80% and 72%, respectively, compared with the untreated specimen. It was further observed that UNSM significantly refined the material grains and considerably increased the martensite. This resulted in a surface microhardness increase of up to 71.2%.

Effects of constrained groove pressing, severe shot peening and ultrasonic nanocrystal surface modification on microstructure and mechanical behavior of S500MC high strength low alloy automotive steel

S500MC high strength low alloy automotive steel is exposed to bulk severe plastic deformation (SPD) via constrained groove pressing (CGP) and surface severe plastic deformation (S2PD) via severe shot peening (SSP) and ultrasonic nanocrystal surface modification (UNSM). SSP and UNSM could create a nanocrystallization layer till 50–100 µm away from outmost surface. EBSD investigations showed average nano-grain size obtained via SSP and UNSM was found to be below 100 nm regime. The strength was improved via 1st to 4th pass of CGP, but elongation percentage decreased abruptly. UNSM achieves both strength-ductility improvement with gradient structure. SSP improves the total elongation however a slight decrease on strength is observed. SSP and UNSM showed better wear and friction resistance particularly at lower loads compared to CGP and untreated specimens. Nevertheless, wear and friction behavior at higher loads showed better responses for Bulk-SPD applications regardless of pass numbers. The frictional load increase played a detrimental role in removing a nanocrystallization surface layer and diminishing the positive influence of SSP and UNSM.

Formation mechanism of hierarchical pattern fabricated by ultrasonic-assisted texturing: dynamic indentation induced pile-up

Ultrasonic-assisted surface texturing can produce surface textures with hierarchical micro/nano-scale structures on metal components. In this work, we prove that the formation of nano-scale structure originates from pile-up produced by ultrasonic dynamic indentation. Both quasi-static and dynamic indentations are performed on pure copper, 316 stainless steel, and pure titanium using an ultrasonic nanocrystal surface modification system. For the first time, it is revealed that ultrasonic dynamic indentation produces significant higher pile-up as compared with that of quasi-static indentation, making nanoscale structure possible. Finite element simulations demonstrate that dynamic indentation produces larger equivalent plastic strain, an indicator for work hardening, in the region close to the edge of the contact interface. It is conjectured that higher degrees of work hardening and dislocation density result in a higher dislocation resistance as compared with quasi-static indentation. The plastic deformation is confined at the contact interface and is then forced to move upward, leading to a significant pile-up.

Surface Quality and Corrosion of Additively Manufactured STS316L Treated by Ultrasonic Nanocrystal Surface Modification

Surface Quality and Corrosion of Additively Manufactured STS316L Treated by Ultrasonic Nanocrystal Surface Modification

A promising post-additive manufacturing surface modification for tailoring gradient nanostructure and harmonic structure in Co–Cr–Mo alloy

In this paper, I tailored a Co–Cr–Mo alloy prepared by additive manufacturing (AM) method to contain both the gradient nanostructure (GN) and harmonic structure (HS) by UNSM (ultrasonic nanocrystal surface modification) at 25 and 500 °C, respectively. The main objective is to characterize the microstructural changes and to evaluate the mechanical properties of GN and HM. Temperature of UNSM played a significant role in controlling the microstructure and strength of GN and HM, where the UNSM-treated at 500 °C sample demonstrated higher strength than those of the as-AM and UNSM at 25 °C samples.

Better Surface Integrity and Tribological Properties of Steel Sintered by Powder Metallurgy.

The current research reports the improvement in surface integrity and tribological characteristics of steel prepared using a powder metallurgy (PM) by ultrasonic nanocrystal surface modification (UNSM) at 25 and 300 °C. The surface integrity and tribological properties of three samples, namely, as-PM, UNSM-25 and UNSM-300 were investigated. The average surface roughness (Ra) of the as-PM, UNSM-25 and UNSM-300 samples was measured using a non-contact 3D scanner, where it was found to be 3.21, 1.14 and 0.74 µm, respectively. The top surface hardness was also measured in order to investigate the influence of UNSM treatment temperature on the hardness. The results revealed that the as-PM sample with a hardness of 109 HV was increased up to 165 and 237 HV, corresponding to a 32.1% and 57.2% after both the UNSM treatment at 25 and 300 °C, respectively. XRD analysis was also performed to confirm if any changes in chemistry and crystal size were took place after the UNSM treatment at 25 and 300 °C. In addition, dry tribological properties of the samples were investigated. The friction coefficient of the as-PM sample was 0.284, which was reduced up to 0.225 and 0.068 after UNSM treatment at 25 and 300 °C, respectively. The wear resistance was also enhanced by 33.2 and 52.9% after UNSM treatment at both 25 and 300 °C. Improvements in surface roughness, hardness and tribological properties was attributed to the elimination of big and deep porosities after UNSM treatment. Wear track of the samples and wear scar of the counter surface balls were investigated by SEM to reach a comprehensive discussion on wear mechanisms. Overall, it was confirmed that UNSM treatment at 25 and 300 °C had a beneficial effect on the surface integrity and tribological characteristics of sintered steel by the PM that is used in a shock absorber for a car engine.

Tribological performance of 52,100 steel subjected to boron-doped DLC coating and ultrasonic nanocrystal surface modification

The tribological performance of AISI 52100 substrates subjected to several surface treatments have been evaluated in rolling, sliding, and mixed mode contact. The surface treatments include a boron-doped diamond-like carbon (B-DLC) coating deposited by plasma-assisted magnetron sputtering, an ultrasonic nanocrystal surface modification (UNSM) technique used to generate severe plastic deformation in the near surface of the steel specimens, and a B-DLC coating applied to a UNSM pretreated surface. In general, the tribological performance of the duplex surface treatment was superior to that of the untreated specimens and of the specimens with the other surface treatments in rolling, sliding, and mixed mode contact. The improved tribological performance of the duplex process was attributed to the combination of increased wear resistance provided by the B-DLC coating and the grain refinement of the martensitic structure of the AISI 52100 imparted by the UNSM process that created a beneficial substrate/coating interface.

Artificial neural network-based prediction model of residual stress and hardness of nickel-based alloys for UNSM parameters optimization

Ultrasonic Nanocrystal Surface Modification (UNSM) is known as one of the surface treatment techniques that utilizes an ultrasonic vibration energy to improve mechanical properties and performance of materials. The dynamic nature of this surface treatment process deforms the top surface and subsurface of materials with a very high strain rate, which makes the direct observation of residual stress and refined layers very difficult. In this study, a novel alternative approach is proposed that is based on the artificial neural network (ANN) concept for predicting residual stress and hardness of various nickel-based alloys that have been subjected to UNSM treatment. Experimental measurement data were used in the ANN training process and validation. The trained model showed the capability of predicting residual stress and hardness accurately with a Pearson correlation value (R) of 0.988 and 0.996, a root mean squared error (RMSE) of 84.231 and 17.028, and a mean absolute error (MAE) of 68.586 and 13.450 for residual stress and hardness models when tested using the test dataset, respectively. It can be concluded that ANN as the alternative approach is a suitable method for accurately performing prediction for practical use in the absence of a mathematical model. Since the experimental result was used in the ANN model training process, the predicted result by the ANN model appears to agree with the experimental results of the UNSM treatment. Because of these demonstration results, the ANN-based prediction model can be used as a tool to optimize the UNSM treatment parameters.

Effects of Ultrasonic Nanocrystal Surface Modification on Mechanical and Corrosion Behavior of LZ91 Mg–Li Alloy

Effects of Ultrasonic Nanocrystal Surface Modification on Mechanical and Corrosion Behavior of LZ91 Mg–Li Alloy

Effects of Surface Severe Plastic Deformation on the Mechanical Behavior of 304 Stainless Steel

In this study, two innovative surface severe plastic deformation (SSPD) methods, namely abrasive waterjet peening (AWJP) and ultrasonic nanocrystal surface modification (UNSM), were applied to a 304 stainless steel to improve the mechanical behavior. The surface roughness, microstructure, residual stress, hardness, and tensile mechanical properties of the alloy after the two SSPD treatments were studied systematically. The results show that both the AWJP and UNSM treatments have greatly positive effects on the mechanical-properties improvements by successfully introducing a hardening layer. Especially the UNSM-processed specimen possesses the most outstanding comprehensive mechanical properties (high strength with the comparable ductility). The yield strength with the UNSM treatment is 443 MPa, corresponding to the 109% and 19% improvements, as compared to that of the base (212 MPa) and AWJP-treated specimens (372 MPa). The results can be attributed to a much thicker hardening layer (about 500 μm) and a better surface integrity with lower roughness (Ra: 0.10 μm) formed by the UNSM technique.

A new guide for improving mechanical properties of non-equiatomic FeCoCrMnNi medium- and high-entropy alloys with ultrasonic nanocrystal surface modification process

Ultrasonic nanocrystal surface modification (UNSM) treatment on non-equiatomic medium- and high-entropy alloy (HEA) of Fex(CoCrMnNi)100-x is firstly introduced and its impact on microstructure and mechanical properties are revealed. By UNSM, severe plastic deformation-induced dislocation and deformation twins (DTs) arise at the topmost surface. Especially, Fe60(CoCrMnNi)40 (Fe60), which is classified as a medium-entropy alloy (MEA), exhibits ε-martensitic transformation. In the room temperature tensile test, a high strength of ∼600 MPa and ductility of ∼65 % elongation (strain to failure) is accomplished in Fe60. Initially formed DTs and ε-martensitic transformation by UNSM treatment plays a key role in retardation of necking point via both twinning-induced plasticity and transformation-induced plasticity. However, Fe20(CoCrMnNi)80 (Fe20) comparatively shows low strength of ∼550 MPa and ∼40 % elongation, owing to the low accommodation of DTs than Fe60. Our research will provide new guidelines for enhancing the mechanical properties of MEA and HEA.

Effect of local treatment temperature of ultrasonic nanocrystalline surface modification on tribological behavior and corrosion resistance of stainless steel 316L produced by selective laser melting

In this study, the effects of local treatment temperature of ultrasonic nanocrystal surface modification (UNSM) on tribological behavior and corrosion resistance of stainless steel 316L produced by selective laser melting (SLM) were investigated. The as-printed samples were treated by UNSM at room and high temperatures (RT and HTs) and their strength, tribological behavior and corrosion resistance were compared and discussed. Dry friction coefficient of the UNSM-treated at RT and HT samples was reduced from 0.73 to 0.56 and 0.67 to 0.52, while the dry sliding wear resistance at RT and HT was enhanced from 7.25 × 10−8 to 5.8 × 10−8 and 7.01 × 10−8 to 5.2 × 10−8 mm3/Nmm, respectively. Increase in local treatment temperature of UNSM resulted a lower friction coefficient and higher wear rate compared to that of the UNSM at RT.

An improvement in fatigue behavior of AISI 4340 steel by shot peening and ultrasonic nanocrystal surface modification

Individual and synergy effects of shot peening (SP) and ultrasonic nanocrystal surface modification (UNSM) on rotary bending fatigue (RBF) behavior of AISI 4340 steel were systematically investigated at various bending stress levels in the range of 275–600 MPa. The results revealed that the fatigue behavior of the as-received sample was enhanced by SP and it was further enhanced by SP and UNSM combination, while the UNSM-treated one exhibited the highest enhancement in fatigue behavior. The fatigue behavior of the SP + UNSM sample was enhanced after SP, but it was found to be detrimental after UNSM. Apart from RBF experiments, individual and synergy effects of SP and UNSM on surface roughness, hardness, residual stresses and grain size were analyzed as well. Fractography of the samples was characterized by scanning electron microscope (SEM) and fatigue mechanisms of each sample were discussed based on the obtained observations. The finest grain size and highest compressive residual stress (CRS) obtained by UNSM in comparison with those of the SP and SP + UNSM was responsible for the best fatigue performance.

Enhancement in microstructural and mechanical performance of AA7075 aluminum alloy via severe shot peening and ultrasonic nanocrystal surface modification

In this experimental study, AA7075 aluminum alloy was subjected to pure severe shot peening (SSP), pure ultrasonic nanocrystalline surface modification (UNSM) and the combination of these two treatments. The treated specimens were analyzed with detailed microstructure analysis, micro-hardness, surface roughness, XRD investigations and wear-friction tests. The results demonstrated that UNSM exhibited fine surface finish and provided minimum surface roughness with the Ra value of 0.8 µm. Moreover, UNSM played an important role in the reduction of Ra as a secondary treatment. Electron back scatter diffraction (EBSD) analysis, full width at half maximum (FWHM) evaluations and compressive residual stress (CRS) measurements showed that the deformed layer structure was converted into a nanocrystallized and compressively stressed zone via SSP and UNSM. The hardness on the topmost layer was effectively enhanced by UNSM + SSP and SSP + UNSM processes. The wear and friction performance were particularly improved by two-stage operations of UNSM + SSP and SSP + UNSM. The performance was also compatible with the hardness, residual stress and nanocrystallization investigations.

The effect of electropulsing-assisted ultrasonic nanocrystal surface modification on the microstructure and properties of 300M steel

In this study, electropulsing-assisted ultrasonic nanocrystal surface modification (EP-UNSM) was used to process 300M steel. It has been demonstrated that pulsed current can more effectively improve the plasticity of 300M steel as compared to continuous current having the same effective current density, even though the bulk temperature (around 150 °C) and thus the thermal effect is the same. It is believed that a pulsed current, which has a much higher peak current density, can more effectively activate pinned dislocations and can better assist the deformation-based surface modification process. EP-UNSM treatment of the steel resulted in much higher surface hardness and greater plastically affected depth as compared to both UNSM and continuous current-assisted UNSM (CC-UNSM). As a result, EP-UNSM treatment imparted much higher wear resistance to the steel than either UNSM or CC-UNSM treatment. It has been demonstrated that pulsed current can effectively improve the process effectiveness of the selected deformation-based surface engineering process (UNSM) without significantly increasing the temperature.

Effects of ultrasonic nanocrystal surface modification on the surface integrity, microstructure, and wear resistance of 300M martensitic ultra-high strength steel

Abstract In this study, the effects of ultrasonic nanocrystal surface modification (UNSM) treatment on the surface integrity, microstructures and wear resistance of 300M ultra-high strength steel (300M steel) were investigated. The results showed that surface roughness of 300M steels after UNSM processing was significantly decreased with a lower scanning speed even though the surface roughness values were higher than that of mechanically polished control samples. In addition, the surface hardness of 300M steel was significantly enhanced as the static load increased. It was found that using a static load of 50 N and a scanning speed of 250 mm/min in the UNSM process can significantly improve surface hardness (797 HV) while slightly increasing the surface roughness. With these parameters, the resulting microstructure of UNSM-processed samples have three layers: the layer of severe plastic deformation, the layer with gradual plastic deformation, and the unaffected layer. Due to the plastic deformation, greater and deeper compressive residual stresses were induced in the UNSM-processed samples. In addition, the wear resistance of UNSM-processed samples was significantly improved, which was attributed to the refined martensite laths, work hardening and compressive residual stress.

Microstructure and mechanical properties of CoCrFeMnNi high entropy alloy with ultrasonic nanocrystal surface modification process

In this study, mechanical properties improvement of equiatomic CoCrFeMnNi treated with an ultrasonic nanocrystal surface modification (UNSM) was studied. The applied UNSM treatment with static loads of 10 N, 20 N, and 60 N provided a severe plastic deformation, which produced a gradient structure. The near-surface area exhibited a high number of dislocation densities and deformation twin interaction, leading to a surface strengthening and hardness improvement of up to 112% than the deformation-free interior region. Increment of dislocation densities and deformation twin formation on the surface also enhanced the yield and ultimate tensile strength of the UNSM-treated specimens. Furthermore, the combination of hard nanocrystallites layer on the surface and ductile coarse grain in the specimen interior as a result of the UNSM treatment successfully maintained the strength–ductility balance of the CoCrFeMnNi.

Mechanical and Tribological Characteristics of Cladded AISI 1045 Carbon Steel.

This study introduces a newly developed cladding device, through printing AISI 1045 carbon steel as single and double layers onto American Society for Testing and Materials (ASTM) H13 tool steel plate. In this study, the mechanical and tribological characteristics of single and double layers were experimentally investigated. Both layers were polished first and then subjected to ultrasonic nanocrystal surface modification (UNSM) treatment to improve the mechanical and tribological characteristics. Surface roughness, surface hardness and depth profile measurements, and X-ray diffraction (XRD) analysis of the polished and UNSM-treated layers were carried out. After tribological tests, the wear tracks of both layers were characterized by scanning electron microscopy (SEM) along with energy-dispersive X-ray spectroscopy (EDX). The surface roughness (Ra and Rz) of the single and double UNSM-treated layers was reduced 74.6% and 85.9% compared to those of both the as-received layers, respectively. In addition, the surface hardness of the single and double layers was dramatically increased, by approximately 23.6% and 23.4% after UNSM treatment, respectively. There was no significant reduction in friction coefficient of both the UNSM-treated layers, but the wear resistance of the single and double UNSM-treated layers was enhanced by approximately 9.4% and 19.3% compared to the single and double polished layers, respectively. It can be concluded that UNSM treatment was capable of improving the mechanical and tribological characteristics of both layers. The newly developed cladding device can be used as an alternative additive manufacturing (AM) method, but efforts and upgrades need to progress in order to increase the productivity of the device and also improve the quality of the layers.

Evaluation of the DOS by DL−EPR of UNSM Processed Inconel 718

In this work, influence of ultrasonic nanocrystal surface modification (UNSM) on the degree of sensitization (DOS) in Inconel 718 has been studied and correlated with the resulting microstructure. The UNSM processed samples decreased their grain size from 11.9 µm to 7.75 µm, increasing the surface of grain boundaries, and thus enhancing the area where δ phase and niobium carbides precipitate. The effect of the UNSM process on the DOS of Inconel 718 was studied by the double loop electrochemical potentiokinetic reactivation (DL−EPR) test. The DL−EPR showed that for UNSM processed samples with no thermal treatment, the DOS increased up to 59.6%, while for UNSM treated samples that were post-annealed at 1000 °C for 10 min and water quenched the DOS decreased down to 40.9%. The increase of grain boundaries surface area and triple junctions after the UNSM process enables the formation of twice the amount of δ phase compared to the as-received Inconel 718 bulk sample. The area fraction of the grain boundary covered by δ phase was of 9.87% in the UNSM region while in the bulk the area fraction was 4.09%. In summary, it was found that after UNSM process, the annealing at 1000 °C for 10 min and water quenching promoted the transformation of γ″ to form δ phase on the grain boundaries, which reduces the intergranular corrosion susceptibility.