Load Scratch Research Articles

Study on Mechanical Cleavage Mechanism of GaAs via Anisotropic Stress Field and Experiments

To satisfy the increasing requirements for high-quality cavity mirrors for semiconductor lasers, the influence of the anisotropic stress field generated by scratching GaAs on the quality of cleavage planes was investigated. First, a novel method for calculating the interplanar spacing was proposed to estimate the favourable direction for the scratching operation. Some mechanical properties in the scratching direction were calculated. Consequently, an anisotropic calculation model of the stress field generated by scratching was established. The calculation model was used to analyse the y-component stress field distribution along different directions beneath the indenter. The results show that the maximum stress occurs at the contact area between the material and indenter tip, and the stress along the <100> orientation is lower than that along the <110> orientation. According to our experiments, a significant decrease in the average radial crack length and a slight decrease in the average kerf width were observed along the [011] direction compared to the corresponding results for the [001] direction. In addition, the (011) plane had a surface roughness of 0.43 nm and could become a preferential cleavage plane under a low scratching load. The results of this study contribute to advance our understanding of the mechanisms of mechanical cleavage processes.

Durable self-cleaning nano-titanium dioxide superhydrophilic coating with anti-fog property

PurposeThis paper aims to design the nano-titanium dioxide (TiO2) coating system which has superhydrophilic property, self-cleaning mechanism and antifog property as well as strong adhesion on glass substrate.Design/methodology/approachTwo hydrophilic materials have been used such as TiO2 nanoparticles as fillers and hydrophilic copolymer, Pluronic F-127 by using simple sol–gel approach. The prepared solution was applied onto glass through dip- and spray-coating techniques and then left for drying at ambient temperature.FindingsThe nano-TiO2 superhydrophilic coating has achieved the water contact angle of 4.9° ± 0.5°. The superhydrophilic coating showed great self-cleaning effect against concentrated syrup and methylene blue where thin layer of water washes the dirt contaminants away. The nano-TiO2 coating exhibits great antifog performance that maintains high transparency of around 89% when the coated glass is placed above hot-fog vapor for 10 min. The fog droplets were condensed into water film which allowed the transmission of light through the glass. The strong adhesion of coated glass shows no total failure at scratch profile when impacted with scratch load of 500, 800 and 1,200 mN.Research limitations/implicationsFindings will be useful in the development of self-cleaning superhydrophilic coating that is applicable on building glass and photovoltaic panel.Practical implicationsThe developed nano-TiO2 coating is developed by the combination of hydrophilic organic copolymer–inorganic TiO2 network to achieve great superhydrophilic property, optimum self-cleaning ability and supreme antifog performance.Social implicationsThe findings will be useful for residents in building glass window where the application will reduce dust accumulation and keep the glass clean for longer period.Originality/valueThe synthesis of nano-TiO2 superhydrophilic coating which can be sprayed on large glass panel and cured at ambient temperature.

Tribological behaviour of a hyperlox coating deposited over nitrided martensitic stainless steel

Martensitic stainless steels are often used in machine components, where are exposed to different solicitations that require good surface properties. Different treatments such as plasma nitriding or coating deposition could be used to improve their wear and corrosion resistance, even combining both methods. In this work, the tribological behaviour of a TiAlN coating with a top layer of TiN, called ‘Hyperlox Gold’, deposited over both nitrided and non-nitrided martensitic stainless steels by PVD PEMS (Physical Vapour Deposition Plasma Enhanced Magnetron Sputtering) was studied. Quenched and tempered AISI 420 martensitic stainless steel was used as base material. A group of samples were plasma nitrided and were subsequently coated. Microstructure of the nitrided layer and the coating were analysed by SEM and XRD. Nanohardness was measured with a Berkovich tip. Wear behaviour was evaluated using pin-on-disk tests (ASTM G99 standard) under three different loads (5 N, 7 N and 10 N) with an alumina ball as a counterpart. Adhesion was evaluated using dynamic conditions such as variable load scratch test and under static condition with Rockwell indentation tests (using 60 kg, 100 kg, and 150 kg). Overall thickness of the coatings was 3.7 μm and their hardness about of 32 ± 2 GPa. The nitrided layer was about 10 μm thick, with a hardness of 17 ± 1 GPa. The coating had good mechanical resistance in sliding adhesive wear conditions under low loads and good adhesion was revealed in a static condition. The presence of a nitrided layer improved the wear behaviour under high loads and the adhesion in dynamic conditions. Critical load was higher for the duplex sample than the coated samples. This work is important for the development of the Argentinian industry where the use of coatings is not largely extended, especially with martensitic stainless steels as substrates.

Mechanical properties and deformation mechanisms of (Ti0.2Zr0.2Nb0.2Hf0.2Ta0.2)C high‐entropy ceramics characterized by nanoindentation and scratch tests

High-entropy carbides ceramics (HECCs) have attracted extensive attention for their broad application prospects in harsh environments, due to the excellent properties. In this work, the (Ti0.2Zr0.2Nb0.2Hf0.2Ta0.2)C HECCs were prepared using spark plasma sintering at 1800 °C. Then, mechanical properties of HECCs were tested by nanoindentation and scratch tests under different loading conditions. Finally, the mechanical properties and deformation mechanisms were discussed in detail. The density of sintered HECCs reached 8.98 g/cm3, with a relative density of 95.63%. The HECCs demonstrated a single-phase with rocksalt microstructures. The elastic modulus of HECCs was almost a constant under different strain rates, while the hardness obviously increased as the indentation strain rate increasing. In addition, a simple fitted formula was developed to establish the function of hardness and strain rate. Under a relative low scratch load, the HECCs exhibited complete elastic–plastic deformation, and the material removal mechanism was plastic deformation. With increasing scratch load, the material removal mechanism of HECCs transformed into the combined action of plastic deformation and brittle fracture. Furthermore, the deformation mechanisms of HECCs were also influenced by the scratch velocity. At a higher scratch velocity, more local fractures at the micro-scale occurred, and the numbers and sizes of chips and debris also increased.

Molecular dynamics study on mechanical cleavage mechanisms of GaAs and experimental verification

Laser bars are fast becoming a key device in a range of specific industrial applications. Mechanical cleavage technology is a new and efficient method for fabricating laser bars. However, there is little detailed analysis of the relationship between scratching step and cleavage step. To close this research gap, a molecular dynamics study on cleavage mechanisms of GaAs are reported investigating surface and subsurface damage, and molecular dynamics method could accurately describe the nano-scale processes in semiconductors at atomic scale. Simulation results show that the scratching depth has a significant effect on the scratch quality as compared with other parameters during the scratching process. Then, a series of cleavage experiments were carried out to verify the simulation results and further explore the influence of key scratching parameters on cleavage plane morphology. Experimental results correlate well with the simulations. Consequently, the achieved optimal combination of parameters have been found to be a scratching load of 10 g, scratching speed of 20 mm/s and scratching length of 0.6 mm, which provides direct guidance for the cleavage processing of GaAs materials. Under optimal conditions, the length and surface roughness of the undamaged area can reach 11.77 mm and 0.43 nm respectively.

Exploring the Effect of Pt Addition on the Fracture Behavior of CrN Coatings by Finite Element Simulation

Previous research confirmed that Pt addition induced a prominent refinement effect of CrN coating, resulting in an enhanced conductivity and corrosion resistance. In this work, a detailed finite element simulation and scratch test were employed to calculate and characterize the fracture failure behaviors (stress distribution, crack damage process, critical coating load, and coating–substrate adhesion energy) of CrN coatings with different Pt contents. Simulation results showed that the synergistic action of dynamic scratch load and extrusion load induced the fracture of the coatings. S11 and S22 caused transverse cracks in the CrN coating, S11 caused longitudinal cracks in the CrN-Pt coating and CrN-3Pt coatings, S22 led to the inclined propagation of cracks in these coatings, and S11 and S22 jointly induced the separation of the coating from the substrate. The doping Pt element in the CrN coating will make the coating easier to fracture and reduce the adhesion strength between the coating and substrate. Scratch test results revealed that adding Pt into the CrN coating will make this coating easier to fracture and cause more serious damage; the simulation results are in good accordance with the scratch test characterizations. The current founding provided a comprehensive understanding for the fracture damage mechanism of Pt-doped nitride coatings.

High transmittance and excellent hardness TiO2‐SiO2‐Al2O3 nanocomposite thin film for anti‐scratch surface applications

AbstractIn this work, TiO2‐SiO2‐x%Al2O3 (x = 0–50) nanocomposite thin films (NCTFs) with high purity, relatively homogeneity, high transmittance, excellent hardness, and crack‐free were synthesized successfully by a spin‐coating technique. It was demonstrated that the transmittance and the hardness of TiO2‐SiO2‐x%Al2O3 NCTFs are strongly affected by the Al2O3 content. The highest transmittance of 90.9% in the visible region (400 to 800 nm) and the excellent hardness and scratch resistance with a maximum hardness value of 7 Mohs and 11.8 GPa of nanoindentation and a critical scratch load of 47.6 mN for the TiO2‐SiO2‐30%Al2O3 NCTF annealed at 500°C in the air for 3 h was achieved. A hardness enhancement mechanism was proposed and discussed in detail. The obtained results show that the fabricated TiO2‐SiO2‐Al2O3 NCTFs have a great potential for anti‐scratch resistance surface applications.

Effect of RF sputtering parameters on the nanoscratch properties of quinary Ti-Zr-Cu-Ni-Al thin film metallic glass

Recently, thin film metallic glasses (TFMGs) gained renewed attention as they can circumvent the brittleness problem of bulk metallic glasses. When sputtered from a multicomponent cast target, the composition control of TFMG is always challenging. Here, we demonstrate the tight composition control of sputtered Ti-Zr-Cu-Ni-Al TFMG by a spark plasma sintered multicomponent target and investigate their structural and nanoscratch properties. The radio frequency (RF) power and Ar pressure were tuned to optimize nanoscratch properties. The highest hardness (~16.2 GPa) and thus best nanoscratch resistance was obtained at an RF power of 160 W and Ar pressure of 7 Pa. The best nanoscratch properties originated from the dense, fine column morphology of the TFMG. Moreover, it was found that the scratch mechanism changed from plowing to a combination of plowing and stick-slip under a ramping scratching load of 10 mN. The transition happened progressively at lower loads when the hardness of the TFMG decreased. This study provides a useful guideline for developing TFMG as a scratch-resistant protective coating. • Multicomponent target fabricated through low-temperature spark plasma sintering allowed precise composition control of TFMG. • A wide range of RF power and Ar pressure (160-240 W and 4–7 Pa) can produce glassy phase in the Ti-Zr-Cu-Ni-Al system. • Optimum nano-scratch resistance and hardness achieved for TFMG deposited at lower power and higher pressure (160 W and 7 Pa).

Scratch-induced deformation and damage behavior of doped diamond-like carbon films under progressive normal load of Vickers indenter

Microscratch test was conducted on four different diamond-like carbon (DLC) films by Vickers indenter to study the scratch resistance of films under progressive normal load linearly increasing from 5 mN to 15 N. With the increase of normal load, penetration depth, lateral force, residual and contact scratch widths increase nonlinearly; scratch hardness and lateral hardness decrease nonlinearly; scratch friction coefficient increases under small loads, and then tends to be a constant under large loads. DLC-H has the smallest scratch friction coefficient among the four films, and different targets have little effect on scratch friction coefficient. DLC-Si and DLC-Cr have almost the same scratch resistance (or penetration depth), and larger than that of DLC, whose scratch resistance is almost the same as that of DLC-H. Fracture toughness was obtained by scratch-based methodologies: the additional Si or Cr target can enhance fracture properties of DLC film-steel substrate systems, whereas C4H10 can harm fracture properties. Fracture toughness of DLC-Si (about 17 MPa·m1/2) was larger than that of DLC-Cr (about 15 MPa·m1/2) with the large values of fracture toughness obtained under penetration depth larger than film thickness attributed to substrate effect.

Effect of Ti/Si and Ti/TiN/Si interlayers on the structure, properties, and tribological behavior of an a-C film deposited onto a C17200 copper-beryllium alloy

Reduced hardness and wear resistance may limit SAE C17200 copper‐beryllium alloy use in manufacturing applications, such as plunger tips of die casting machines and as cores and inserts for steel dies in injection molding processes. In order to improve the surface properties of Cu—Be alloys, amorphous carbon (a-C) films have been selected since these coatings may show high hardness, low wear rate and low coefficient of friction. However, the adhesion of carbonaceous films on Cu—Be alloys remains a challenge. Two interlayer compositions (Ti/Si and Ti/TiN/Si) were deposited onto Cu—Be disks and silicon wafers to assess amorphous carbon adhesion on substrates made of Cu—Be alloy. The microstructure and topography of the coatings were examined by Field Emission Scanning Electron Microscopy (FESEM) coupled with X-ray dispersive energy spectroscopy (EDS). The chemical composition depth profile was measured by glow discharge optical emission spectroscopy (GDOES), which confirmed distinct coating layers of Ti, Si, a-C (C1 and C2 conditions-pDCMS). A TiN extra layer presence was obtained for the C3 and C4 conditions-pDCMS reactive, confirmed by small angle XRD analysis. Raman scattering spectroscopy showed a higher quantity of sp3 carbon bonds for C3 and C4 coating conditions compared to C1 and C2. Instrumented indentation tests indicated a higher hardness and reduced elastic modulus for C3 and C4 coating systems, corroborating Raman results, in terms of a higher concentration of sp3 bonds. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and coherence correlation interferometry (CCI) were used to characterize the coatings' surface features and scratch tracks after the tests. In addition, ramp load scratch tests were conducted to assess coating adhesion to the Cu—Be alloy substrate by measuring critical loads and the coefficient of friction. The highest critical loads to failure (Lc2) and (Lc3) were found for the Ti/TiN/Si interlayer sample (C4 condition), indicating that this interlayer improved the coating contribution to a gradual increase in the hardness and promotion of an enhanced adhesion strength of the a-C coating.

Contact size effects on the friction and wear of amorphous carbon films

Since different properties of coating systems influence their friction and wear at different length scales contact size can play a critical role in microtribological experiments. In this study the behaviour of 3 different types of coating system which vary in terms of their thickness, substrate and mechanical properties has been investigated. The coatings were chosen for either their industrial relevance in automotive or MEMS applications, or as model coating systems. A wide range of nano/microtribological tests have been performed with different indenter geometries (tip sharpness), including single and repetitive scratch tests with unidirectional contact, and reciprocating wear tests, with depth and friction evolution monitored so that the relationships between failure mechanism and friction in coating systems with differing mechanical properties could be explored. The influence of surface topography on friction has been shown in ramped and constant load scratch tests. When fracture occurred resulting in a sudden increase in probe depth there was an abrupt decrease in friction which is ascribed to a contact area effect. In contrast, where deformation progressed through micro-wear a more gradual increase in depth can be associated with higher contact area and higher friction.

Investigation of AlN ceramic anisotropic deformation behavior during scratching

To explore the anisotropic deformation behavior of aluminum nitride ceramic during processing, ramp and constant load scratch experiments were conducted with Vickers indenter. Characteristics of deformation anisotropy were observed in ramp-load scratch with differences found in the directions of pile-ups, slip lines and cracks produced by grains with various orientations. Constant-load scratches were conducted to explore the anisotropic deformation behavior in plastic stage. Obvious differences were found in scratch pile-up height and residual depth of grains with different orientations. As the grain orientation Euler angle changes from the basal to the two prism surfaces, the residual depth of the scratch gradually increases. Molecular dynamics simulation was performed to disclose the mechanisms of anisotropic dislocation and deformation during scratching. The activation of the slip system for different grain orientations was calculated by a scratch Schmid factor model which was verified by the observation of pile-ups and slip lines around the scratches.

Microscale friction and deformation behavior of polydopamine/polytetrafluoroethylene-coated 60NiTi from nanoscratch tests

The scratch behavior of polydopamine (PDA)/polytetrafluoroethylene (PTFE) coatings has traditionally been studied using macro-scale tribometers. However, in this study, a nanoindenter is used to scratch PDA/PTFE coatings on 60NiTi substrate to investigate the nanoscale deformation behavior and failure mechanisms of this coating under various scratch loads. Nanoscratch tests were also performed on the substrate coated only with the adhesive underlayer to study the behavior of PDA under various scratch loads. Scanning electron microscope imaging of the scratches provided further insights to the coating scratch deformation behavior. The study revealed the PDA/PTFE coating failure is strongly correlated with the removal of the PDA particles in the underlayer. The findings also suggest that the compaction of the thin PDA/PTFE coatings could be the main reason for the previously reported large initial wear depth in macro-scale tribology studies.

Improved tribological properties of stainless steel by high temperature-alloyed tantalum gradient layer

Tantalum (Ta) gradient transitional layer, which was prepared by double-glow plasma surface alloying technology, was designed to improve the tribological properties of AISI 304 stainless steel. The microstructure, morphology, mechanical and tribological properties of surface modified stainless steel were characterized and analyzed. The results showed that the modified Ta coating can improve the surface roughness and tribological properties of the AISI 304 stainless steel greatly. Furthermore, β-Ta is in the majority in gradient transitional layer and it show high critical scratch load. The thickness of Ta coating, surface roughness, load bearing capacity, friction coefficient and wear rate of Ta/AISI 304 increased first and then decreased. Especially, the sample with Ta alloyed time of 30 min show excellent tribological properties, which were closely related with high critical load, low surface roughness, and the phase transformation from metastable β-Ta to stable cubic α-Ta in less oxygen conditions at the role of frictional heat. Furthermore, there are α-Ta nanoparticles with assembled into nanoribbons on the counterface decreasing the friction and wear further. The present study provides useful guidance for the modification of AISI304 and a new prospect on the transition from β-Ta to α-Ta during the friction.

Scratch resistance of cobalt boride layer subjected to a diffusion annealing process

This work studies the effect of a diffusion annealing process in cobalt boride layers by progressive load scratch (PLST) and multipass scratch (MPST) tests. First, a double-phase CoB/Co2B layer was formed on CoCrMo alloy at 1000 °C for 6 h. Next, a single-phase Co2B layer was obtained through a diffusion annealing process. The scratch tests were conducted with a progressive load from 5 to 150 N in PLST, whereas in MPST, up to 400 passes were applied with a subcritical load of 38 N. Conducting the diffusion annealing process significantly improved the scratch resistance; in PLST, the achieved layer avoided severe failure mechanisms and decreased residual depth by 60%. In MPST, friction was reduced and the volume loss decreased around 50%.

Effect of scratch depth on high cycle fatigue behavior of Alloy 690TT stream generator tube

The effect of scratch depth on high cycle fatigue behavior of Alloy 690TT stream generator (SG) tubes was investigated by experimental characterization and numerical simulation. Results indicated that fatigue cracks initiated at the scratch root of the SG tube external surface. The effect of scratch depth on fatigue life mainly depended on the loading stress levels, which could be considered as an exponential relationship between the loading stress and scratch depth for a given fatigue life. The fatigue limit decreased with the increase of scratch depth and changed in a small range of yield strength.

The Effect of Al and Ti Transition Metals on the Wear Resistance of Ceramic Based CrN Coatings; Investigation under Ambient Air and Vacuum Conditions

In the present study, CrN, CrAlN and CrAlTiN coatings were deposited using the cathodic arc evaporation technique. The structural investigations of these CrN based coatings were performed by scanning electron microscopy, energy dispersive spectroscopy, atomic force microscopy, X-ray diffractometer. The hardness and adhesion strength values of coatings were determined via Vickers type microhardness tester and progressive load scratch tester, respectively. The wear performance of samples was established at ambient air and vacuum condition. All coatings grew in the “T zone” growth model and had a dense and columnar structure. The XRD patterns presented predominantly (220), (110), and (111) reflections. It was demonstrated that the quaternary coating had a higher texture parameter as 0.68, which was related to the highest thickness and hardness. Also, CrAlTiN coatings with the smallest mean crystallite size of ∼87 nm showed the best hardness, and this ensured relatively high scratch resistance. CrN and CrAlTiN coatings improved wear performance under ambient air condition but were not striking as under vacuum condition. The quaternary coating had a superior performance in the vacuum condition, but due to the high sensitivity of Ti to oxygen, it fell behind the CrN coating under ambient air condition.

Energy consumption analysis of different scratching methods in GaAs mechanical cleavage processing

High performance and low energy consumption are major priorities for modern manufacturing techniques. In order to improve the quality of cleavage planes while reducing energy consumption, this paper presents an experimental investigation of energy savings during the mechanical cleavage process using different scratching methods. According to the simulation results, an improved scratching method, dot scratching, gave a scratching length of approximately 0.6 mm. The scratching energies of the traditional scratching method and the dot scratching method along the <100> and <110> directions were calculated and analysed from the perspective of energy consumption. A series of scratching and cleavage experiments were carried out to investigate the features on scratch and cleavage surfaces. The experimental results for the scratching procedure showed that scratching along the <110> direction using the dot scratching method is beneficial for reducing the maximum damage width of gallium arsenide (GaAs). The dot scratching method can significantly reduce energy consumption during the cleavage of GaAs, and the energy saving ratios exceed 70%. A flat cleavage plane can be obtained by cleavage using the dot scratching method under a lower scratching load. Adoption of the dot scratching method thus has the potential to improve the efficiency and quality of cleavage processes and offers a practical solution for the greener manufacturing of semiconductor cleavage planes.

Sliding indentation: failure modes with study of velocity and loading rate

Scratch tests were done at micro and nano scale to study the adhesive strength of the SiCN coatings deposited by magnetron sputtering. SiCN are nanocomposites having different hard phases making them useful as protective coatings. The nature of coating/substrate system got reflected in the failure modes in the scratch track. Nano scratch consisted of a three stage process viz. pre scan, scan and post scan for the elastic recover. Effect of scratch velocity and load were studied. The results give an insight into the behavior of the coating subject to different mechanical conditions and hence its suitability for a particular use.

Scratch behavior and mechanical properties of alternating multi-layered PMMA/PC materials

Poly (methyl methacrylate) (PMMA)/polycarbonate (PC) laminates have been widely used as backboards for 5G cellphones where surface aesthetics are required. For this reason, the scratch behavior of the material is of particular interest. In the present work, the scratch behavior of alternating multi-layered PMMA/PC materials was studied by progressive normal load scratch tests and finite element modeling (FEM). The experimental results showed that interfacial delamination between the PMMA and PC layers occurred after the onset of scratch damage. The detailed delamination process and related mechanisms were revealed by FEM. It was found that interfacial delamination during scratching can be divided into three successive stages: delamination initiation, delamination expansion, and delamination propagation. All stages were revealed to be dominated by shearing mode (Mode II & III) crack propagation, while opening mode (Mode I) crack propagation was not involved. Furthermore, the mechanical results demonstrated a dramatic enhancement of ductility and toughness when the number of layers was increased.