Single Scratch Research Articles

Effect of carbide orientation during single scratch test in directionally solidified and heat-treated high chromium cast irons

In this work, a billet of eutectic high chromium cast iron, material commonly used in highly abrasive environments, such as in grinding and milling, was unidirectionally solidified. The resulting microstructure was composed of oriented M7C3 carbides and eutectic matrix. Specimens were cut parallel and transversally to the billet axis and split into two groups. Both were heat treated with different austenitization temperatures. The temperature for the first group was 1100 °C, and the value for the second was 950 °C, providing matrix instrumented indentation hardness values of 8.0 and 6.3 GPa, respectively. This procedure resulted in specimens with three carbide directions dispersed in two different matrices. Samples were evaluated by means of single scratch test with a cono-spherical diamond stylus under progressive and constant normal load conditions. To support the analysis, a non-contact 3D surface profiler and scanning electron microscopy (SEM) were used to characterize the scratched surfaces. Progressive load tests indicated a transition in wear micro-mechanisms which was mainly observed in the samples with the long axes of the carbides parallel to the wear surface and oriented orthogonal to the scratch direction and with matrix hardness of 6.3 GPa. On the other hand, constant load tests showed that carbides with the long axes parallel to the wear surface and oriented parallel to the scratch direction tend to produce deeper scratchers with higher ridges than in the other directions. Results also indicate that the hardness, despite being an important variable, does not entirely explain the behavior of the material under single scratch, since the orientation of the carbides with respect to the scratch direction must also be considered.

Subsurface damage model in single and double scratching of fused silica with a blunt indenter

The subsurface damages (SSDs) generated during abrasive processes greatly impact the service performance and life of the devices or components made from brittle materials. The abrasive processes can be simplified as multi-scratching where the abrasive grits tend to be blunt. Consequently, the evaluation of SSDs in the scratching with a blunt indenter is worth of study. In this paper, by extending the blunt indenter-related indentation fracture mechanics and deriving the analytic equations for the contact areas between the indenter and the workpiece, a theoretical SSD depth model is first developed for the single and double scratching of brittle materials. The model correlates the depth of subsurface cone, median, and lateral cracks with the indenter nose radius, scratching depth, residual depth, normal load, tangential load, scratch spacing, and workpiece material properties. To validate the model, scratching experiments are carried out on polished fused silica under different scratch spacing, and the effects of scratch spacing on the surface/subsurface morphologies of scratch grooves, scratching load, and friction coefficient are investigated experimentally. The results show that the radial, cone, median, and lateral cracks are coexistent in fused silica. The second scratching leads to an increase in the fracture degree of the first one, while the SSD depth in double scratching approximates that in single scratching. A small scratch spacing leads to an increase in tangential load or friction coefficient while a decrease in normal load. It is proven that the theoretical model can accurately determine the upper/lower bounds of scratching normal load and subsurface crack depth considering the workpiece fracture degree. Moreover, it is revealed that the SSD depth increases slightly with an increased friction coefficient. This research contributes to the evaluation of SSDs in the abrasive-processed fused silica or similar brittle materials.

Stress corrosion cracking of 316LN stainless steel with orthogonal scratches

316LN stainless steel is used to produce the third generation primary circuit pipe of pressurized water reactor (PWR). Its internal and external pipe surfaces are generally introduced with scratches when manufactured, transported and installed processes, making their research and discovery on the stress corrosion cracking (SCC) sensitivity challenging. In the present study, multiple orthogonal scratches on 316LN stainless steel are prepared using the rotary cutting head. The effects of the orthogonal scratches on the SCC of 316LN stainless steel are investigated. The experimental results show that the force bearing point of this kind of rotary cutter head is near 60° on the side, which is different from the common cutter head. At the intersection of orthogonal scratches, larger strain concentration and more oxide particles can be formed comparing with single scratch. With increasing strain concentration, the more nucleation sites and the greater growth driving force for the oxide particles can be formed. Thus larger and more oxide particles in this case are generated, resulting in finally a greater SCC sensitivity.

Fiber orientation effects on grinding characteristics and removal mechanism of 2.5D Cf/SiC composites

Carbon fiber reinforced silicon carbide (Cf/SiC) composites are widely used in aerospace for their excellent mechanical properties. However, the quality of the machined surface is poor and unpredictable due to the material heterogeneity induced by complex removal mechanism. To clarify the effects of fiber orientation on the grinding characteristics and removal mechanism, single grit scratch experiments under different fiber orientations are conducted and a three-phase numerical modelling method for 2.5D Cf/SiC composites is proposed. Three fiber cutting modes i.e., transverse, normal and longitudinal, are defined by fiber orientation and three machining directions i.e., MA (longitudinal and normal), MB (longitudinal and transverse) and MC (normal and transverse), are selected to investigate the effect of fiber orientation on grinding force and micro-morphology. Besides, a three-phase cutting model of 2.5D Cf/SiC composites considering the mechanical properties of the matrix, fiber and interface is developed. Corresponding simulations are performed to reveal the micro-mechanism of crack initiation and extension as well as the material removal mechanism under different fiber orientations. The results indicate that the scratching forces fluctuate periodically, and the order of mean forces is MA > MC > MB. Cracks tend to grow along the fiber axis, which results in the largest damage layer for transverse fibers and the smallest for longitudinal fibers. The removal modes of transverse fibers are worn, fracture and peel-off, in which normal fibers are pullout and outcrop and the longitudinal fibers are worn and push-off. Under the stable cutting condition, the change of contact area between fiber and grit leads to different removal modes of fiber in the same cutting mode, and the increase of contact area results in the aggravation of fiber fracture.

Investigation of material removal mechanisms of laser-structured Si3N4 via single diamond grit scratching

Grinding hard-brittle materials like silicon nitride is faced with some challenges, including sub-surface damage, high tool wear, and low grinding efficiency. Ultrashort-pulse laser structuring of hard materials prior to the grinding process significantly reduces the cutting forces and temperature and increases the achievable material removal rate of the grinding process. These effects are partially due to controllable induced damages into the subsurface of the structured workpieces. However, the impacts of this surface structuring technique on the material removal mechanism of advanced ceramics, such as Si3N4, are not yet thoroughly investigated. The dominant material removal mechanism in grinding hard and brittle materials, such as silicon nitride (Si3N4), defines the surface integrity of the workpiece. For the first time, in-depth single diamond grit scratching experiments are carried out to investigate the changes in the dominant material removal mechanisms at various chip thicknesses by laser structuring of Si3N4. Two different structuring ratios (25% and 50%) were generated on sample surfaces by a femtosecond laser. The effects of laser structuring on material removal mechanism, pile-up area, area and width of the groove, grit path, normal and tangential forces, and specific cutting energy have been investigated. The results indicate that laser structuring considerably affects the reduction of depth ratio, normal (up to 89%) and tangential (up to 82%) forces, and specific cutting energy. The specific cutting energy of laser-structured Si3N4 workpieces converged to about 5 J/mm3, much lower than that of unstructured workpieces.

Investigation of the effects of reinforcement particles in polymers on their grindability in single grit scratch test

Recently, polyether ether ketone (PEEK) and its particle-reinforced composites have found a special place in various industries due to their high strength-to-weight ratio, anti-allergic properties, high resistance to buckling, and other superior properties. These materials have widely been used in the aerospace and medical industries and are commonly finished in the final step through the grinding process. In this work, the single grain scratch test was performed to fundamentally study the grinding process and material removal mechanism of PEEK and its particle-reinforced composites. In this method, the material removal is realized by a single grit penetrating the workpiece. It was found that the amount of flowed or piled-up (side flow) materials around the scratch in the pure polymer is higher than the other two composites. Pure polymer with 2.5 J/mm3 and glass fiber-reinforced composite with 1.1 J/mm3 resulted in the highest and lowest specific energies, respectively. The specific energy of all three materials is reduced significantly by increasing the grit penetration depth, showing the significant role of the size effect in grinding these materials. The main reasons for the different results are the high heat transfer coefficient and higher strength of CFRP composite compared to PEEK and PEEK GF 30.

Corneal stromal demarcation line depth after corneal collagen cross-linking following conventional versus customized corneal epithelial debridement

Aim of the Study: Using anterior segment optical coherence tomography (AS-OCT) to compare the depth of corneal demarcation line (DL) after corneal collagen cross-linking (CXL) with subtotal versus customized corneal epithelium debridement. Design: Prospective multi centric case-control study. Materials and Methods: The study enrolled 18 patients with bilateral progressive keratoconus. Both eyes treated by CXL using 3 mW/cm2 / 30 minutes setting. One eye with subtotal epithelial debridement ( about 9 mm diameter) and the contralateral eye with customized debridement ( approximately 1 mm single horizontal scratch ). One month postoperatively, patients had AS-OCT imaging to detect and measure the depth of DL. Results: Patients’ age mean was 25.17 years +/- 4.81 SD . Epithelial healing completed with in 3-7 days in conventional treatment group and demarcation line was evident in 16 eyes ( 89% ) with a mean depth of 290.31 micro m while in customized epi-off treatment group, the epithelial healing lasted less than 24 hours and DL was detectable in 10 patients ( 55.5 % ) with a mean DL depth of 221 micro m with a statistically significant difference ( p < 0.05 ) Subjective postoperative pain graded as “moderate to severe” in about 77% of eyes underwent 9 mm epi-off CXL compared with 55% of those with customized treatment. Conclusions: Although the DL if found in majority cases, but the shallow location in customized corneal debridement cases questioned the efficacy of this technique despite the quick re-epithelialization and less postoperative pain that accompanied it.

Experimental study and smoothed particle hydrodynamics simulation of synthetic diamond grit scratching on steel

Superabrasives like synthetic diamonds are indispensable in today’s construction industry, particularly for core drilling applications in reinforced concrete. The increase of the cutting efficiency of such core bits strongly depends on the material removal behavior of single diamond grains placed in a diamond segment acting as cutting elements. Therefore, this paper presents a newly developed experimental setup for a 3-mm single diamond grain scratch test, as well as the application of a Smoothed Particle Hydrodynamics (SPH) method to model single diamond grains scratching a rebar base material at operational parameters. Diamonds in two main different crystallographic and geometric orientations are tested and investigated with respect to their forces and temperatures at the cutting edge. Furthermore, the chip formation and different material removal mechanisms are analyzed for each orientation and compared with the model output. Validation tests and sensitivity analyses are performed in 3D and high resolution, thanks to the runtime acceleration of SPH through parallel computing on the graphics card. The results indicate: 1) A significantly different material removal behavior as a result of changing the diamond orientation; 2) The capability and high efficiency of SPH for modeling single grain scratch tests.

Influence of cooling kinetics on surface texture, hydrophilicity and scratch resistance of the oxide layers produced by thermal oxidation on Ti-6Al-4V

BackgroundThe properties like high strength to weight ratio and superior corrosion resistance made Ti-6Al-4V as one on the most sorted alloy among titanium alloys for the manufacturing of orthopedic and other implants. Despite these characteristics, it is accompanied by disadvantages like lower wear resistance, release of metal ions due to degradation of passive oxide layer present on the alloys causing allergic reaction to patients. This limits their application to non-articulating joints and long-term stability of the simplant is uncertain. Surface modification through different techniques is considered as viable solution to overcome the above limitations. MethodSurface modification in the present study is carried out using thermal oxidation technique. Titanium dioxide (TiO2) layers were synthesized over the surface of Ti-6Al-4V substrate using thermal oxidation technique. The polished Ti-6Al-4V substrates were subjected to oxidation for 24 h at a temperature of 650 °C in a muffle furnace. The specimens are then brought to room temperature using furnace cooling, air cooling and oil cooling. The resultant oxide layers were characterized for surface morphology, oxide layer thickness, crystalline phase, chemical composition, wettability, surface texture, hardness, and adhesion strength. ResultsThe sample subjected to oil cooling had least Sa of 0.107 μm and highest contact angle of 118.64 ± 2.53° leading to hydrophobicity. The furnace and air-cooled samples had similar Sa of 0.135 μm and 0.134 μm leading to contact angles of 78.28 ± 1.56° and 84.11 ± 1.51° which are hydrophilic in nature. The surface of the oil-cooled samples is dominated by TiO2 when compared to other oxides. The adhesion strength of the oxide layers developed was investigated by using single point progressive scratch test. The influence of surface texture, chemical nature on hydrophilicity and adhesion strength were examined.

Modeling Grinding Processes—Mesh or Mesh-Free Methods, 2D or 3D Approach?

The objectives of this study are mainly two: (1) to validate whether a single grain scratch process can be modeled in two dimensions under the assumption of plane strain, and (2) to select the best discretization approach to model a single grain scratch process. This paper first focuses on the simulation of the orthogonal cutting process (aluminum alloy A2024 T351) using two mesh-based discretization approaches, the pure Lagrangian method (LAG) and the arbitrary Lagrangian–Eulerian method (ALE), and two particle-based approaches, the particle finite element method (PFEM) and smooth particle hydrodynamics (SPH), for both positive and negative rake angles. Benchmarking of the orthogonal cutting models at a rake angle of γ=20∘ is performed with the results of the process forces (cutting and passive forces) of a turning experiment from the literature. It is shown that all models are able to predict the cutting forces, but not the passive force. The orthogonal cutting model is further extended to simulate the cutting mechanism with negative rake tool geometries typically found in grinding and single grit scratching processes. The effects of the negative rake angles on the discretization approaches are studied. The calculated process forces are also compared to the measurements of the single grit scratch process performed at our laboratory. The 2D orthogonal cutting models significantly overestimate the process forces. One of the reasons why the orthogonal 2D cutting model is inadequate is that it cannot describe the complex mechanisms of material removal such as rubbing, plowing, and cutting. To account for these phenomena in LAG, ALE, and SPH discretization approaches, a 3D scratch model is developed. When comparing the process forces of the 3D model with the experimental measurements, all three discretization approaches show good agreement. However, it can be seen that the ALE model most closely matches the process forces with the experimental results. Finally, the ALE 3D scratch model was subjected to sensitivity analysis by changing the cutting speed, the depth of cut and the tool geometry. The results clearly show that the ALE method not only predicts the process forces and form the trends observed in the scratching experiments, but also predicts the scratch topography satisfactorily. Hence, we conclude that a 3D model is necessary to describe a scratch process and that the ALE method is the best discretization method.

Gross fracture pits at the intersection of two single scratches during grinding of silicon

Infeed grinding is used in the industry for grinding thick silicon wafers. The grinding process being a series of overlapping scratches, leaves behind the surface and sub-surface damages in the silicon. Continuous in-feed grinding of a thick wafer when used to produce thin wafer leads to breakage upon release from the fixture. This happens because of not only damage induced by a single scratch, but also due to cumulative damage induced as the grinding proceeds with several overlapping and intersecting scratches. In a single scratch, depths below a critical depth can cause material removal without gross fracture and pits; however, it is not clear if this applies to multiple intersecting scratches while grinding silicon. In this study, the grinding operation is performed for a very short period of time, gradually removing the material over only a partial region of the wafer surface while leaving the remaining portion unground. This produces multiple intersecting grinding scratches of increasing depth. Scanning electron microscopy and surface profile measurements of these scratches show that while in a single scratch, material is removed without gross fracture and pitting; when two such scratch intersects, it results in gross fracture at the site of their intersection. Such gross fractures at intersections can happen even at a very shallow depth of scratch as low as 28 nm. This gross fracture at the intersections act as local sites to initiate wafer damage and material removal. Based on the results, we attempted to redefine the critical depth of cut for grinding operation. The study paves the way to manufacture thin damage-free wafers needed for the next generation thin silicon solar cells.

Understanding the surface generation mechanism during micro-scratching of Ti-6Al-4V

A lot of grinding research in the past has been emulated using single grit scratching. This limits studying surface generation mechanism due to overlapping scratches inherent to the grinding process. It not only affects the surface generation mechanism, but also limits studying elastic recovery which has a significant effect on the final form and topography including the roughness generated after grinding. Taking Ti-6Al-4V as a testbed, this investigation was directed on comparing single scratches with adjacent scratches, which are often referred to as double scratches in literature. During the experiments, the effect of scratch speed and the scratch separation distance on the cutting forces, material pile-up area ratio (PA), groove depth, material removal area (MRA), and sub-surface deformation were investigated. It was found that the scratch speed significantly affects the pile-up and groove depth because of phenomena like stress build-up and elastic recovery. A complementary analytical model of ploughing and shearing forces developed here led to the observation that the minimum chip thickness can only be around 0.1 to 0.2 times the radius of the indenter. Elastic recovery was found to be larger at the middle of the scratch, which was confirmed by the stress-strain relations derived from the FEM simulations. It was also observed that the spacing between two subsequent scratches can significantly affect the scratched surface quality. These experiments show that the severe ploughing and mid-region ridge features can be avoided by having the scratch pitch to be at least one third of the grit tip radius.

Effect of grinding damage on cutting force and ductile machining during single grain scratching of monocrystalline silicon

Understanding the initiating and suppression mechanisms of existing defects are the key to optimizing the ultra-precision grinding process of hard and brittle materials. This paper discusses the effects of grinding damage on material removal mechanism from the perspectives of residual scratch depth, scratch morphology and normal scratching force, through conducting the contrast variable-depth nano-scratch experiment on polished and ground monocrystalline silicon and establishing the single grain scratching Smoothed Particle Hydrodynamics (SPH) model. The experimental and simulation results show that radial crack on ground silicon surface is almost invisible due to the existence of grinding marks, which indicates that it is difficult to judge the ductile brittle transition (DBT) point by the traditional method of observing cracks. With the increase of penetration depth, pop-in will occur in the residual scratch depth of polished and ground silicon, indicating that the material removal mode has transformed, which provides an important basis for judging the DBT point. The DBT critical normal scratching force (38.93 mN) and residual scratch depth (−0.14 μm) of ground silicon are much higher than those of polished silicon, implying ground silicon is easier to achieve ductile processing. Meanwhile, when the penetration depth is the same, compared to polished silicon, the normal scratching force of ground silicon is generally larger. Finally, a single grain scratching SPH model of pre-stressed silicon is established. And the simulated phenomenon and conclusions are consistent with the experiment, which proves that the surface compressive stress is an important factor that causes the removal characteristics of ground silicon to be different from polished silicon. This study provides a theoretical basis for understanding the ultra-precision grinding removal mechanism of hard and brittle materials.

Microstructural origin of high scratch resistance in a gradient nanograined 316L stainless steel

Surface gradient nanostructures can be implemented in metallic materials to offer outstanding resistance to sliding friction and wear, but their scratch resistance and underlying anti-scratch mechanisms remain unknown. In this study, the scratch behavior and linked structure modification of a gradient nanograined 316L stainless steel were investigated and compared to the coarse-grained and the nanograined counterparts. After a single high-load scratch, inhomogeneous nanostructures are formed ahead of the indenter in the coarse-grained and nanograined samples, predominantly leading to mechanical incompatibility, crack nucleation and subsurface peeling-off. By contrast, the gradient nanograined sample exhibits superior scratch resistance without surface and subsurface cracking, thanks to strain delocalization associated with stabilized gradient nanostructure during scratching. This work forges the links between scratch-induced microstructural origin and high scratch resistance for gradient nanograined materials under extremely high tribological stress.

Surface Morphology Evaluation and Material Removal Mechanism Analysis by Single Abrasive Scratching of RB-SiC Ceramics

Reaction-Bonded Silicon Carbide (RB-SiC) ceramics possessing excellent mechanical and chemical properties, whose surface integrities have an essential effect on their performance and service life, have been widely used as substrates in the core parts of aerospace, optics and semiconductors industries. The single abrasive scratching test is considered as the effective way to provide the fundamental material removal mechanisms in the abrasive lapping and polishing of RB-SiC ceramics for the best surface finish. In this study, a novel single abrasive scratching test with an increasing scratching depth has been properly designed to represent the real abrasive lapping and polishing process and employed to experimentally investigate the surface integrity regarding different scratching speeds. Three typical and different material removal stages, including the ductile mode, ductile–brittle transition mode and brittle mode, can be clearly distinguished and it is found that in the ductile material removal stage by increasing the scratching speed would inhibit the plastic deformation and improve its surface integrity. It is also found that in the ductile–brittle transition and brittle material removal stages, to increase the scratching speed would inhibit the plastic deformation due to the fast scratching speed that limits the time of plastic deformation on the target, but it also results in the increased length of lateral cracks with the increased scratching speed which can reflect that the size of brittle chips, like brittle fractures and large grain fragmentations, increases as the scratching speed increases. It can provide the references for the optimization of the abrasive lapping and polishing of RB-SiC ceramics with high efficiency and surface quality.

Investigation on scratching force and material removal mechanism of 3D SiCf/C–SiC composites during single grain scratching

As one of the novel fiber-reinforced ceramic matrix composites, SiCf/C-SiC composites are difficult to machine materials and the material removal mechanism is not completely clear yet. Single grain scratching tests with gradual depth have been carried out to analyze the influence of fiber orientation and woven structure on the material removal mechanism and scratching force in three typical scratched surfaces defined by the fiber orientation. Results indicate that the scratching force waveform is affected by the weaving method, fibers orientation, and porosity distribution of the scratched area, resulting in periodic fluctuations. Diamond indenter causes greater damage to the surface of SiCf/C-SiC composites when scratching along transverse fibers, while leaving narrow but deep grooves on the surface when scratching along perpendicular fibers. The dominant mode of material removal of SiCf/C-SiC composites is brittle fracture, and the damage features mainly include direct fiber breakage, matrix fragmentation, fiber pullout, fiber outcropping.

Investigation of friction and wear resistance of carbonitrided AISI 4130 steels using single and multi-pass scratch technique

The present paper investigates the friction and wear resistance of carbonitrided AISI 4130 steels using single and multi-pass scratch techniques. The influence of carbon concentration in high-temperature gas carbonitriding on friction, wear, and corrosion behavior was studied. The microstructure and morphological properties of carbonitrided layers were investigated employing optical microscope and XRD. The corrosion performance of carbonitrided layers was also evaluated using potentiodynamic polarization in 3.5 wt.% aqueous solution of NaCl. The results of microstructure showed the formation of an arrangement of carbonitrides, chromium nitride, retained austenite, and [Formula: see text] carbides phases in the carbonitrided layers. The carbonitrided layer microhardness increased as a function of increasing carbon concentration to attain a maximum value of about 980 HV0.1 at a carbon content between 1 and 1.2%. The microhardness value was more than 3 times than those of the untreated AISI 4130 steels. Moreover, carbon content has a significant influence on the scratch resistance. For single pass, a critical load (LC1) of about 3.5 N was found. The use of multi-pass scratching allowed to examine friction coefficient, wear volume, and damage mechanism. Carbonitrided layers revealed a low friction coefficient (0.06) and a low wear volume that does not exceed [Formula: see text]. Moreover, the multi-pass scratch technique can extract valuable information about the wear behavior of the carbonitrided layers. The results of corrosion test showed that the formation of [Formula: see text], [Formula: see text] and chromium nitride phases in carbonitrided layers were at the origin of high electrochemical resistance.

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.

Simulation of a Diamond Grain Interaction with Ceramics Using the Smoothed Particle Galerkin Method

The article presents the results of a single grain scratching simulation of a ceramic workpiece using the smoothed particle Galerkin method. The studies were carried out for 0.1-0.8 μm depths of cut, matching the ductile-brittle transition of ceramics grinding with minimum subsurface damage. The crack depth and scratching force were obtained for scratching speed of 40-140 m/s.

Effect of diisocyanate structure on steric restructuring of hindered urea bonds for self-healable coating

Hindered-urea bonds (HUBs), made of bulky amine and isocyanate, are reversible and the reversibility generally comes from the steric hindrance of the bulky substituents on the amine. In this study, the steric effects of diisocyantes (DIs) on the reversibility of HUBs and HUB-bearing polymers were studied. An acrylic prepolymer bearing tertiary-butyl amine (PtB) was prepared and crosslinked with five different DIs. The reversibility of the HUBs as well as the thermodynamic and self-healing behaviours of the HUB-bearing polymer networks (PtB-DIs) were investigated with respect to the structure of alkyl substituents on DIs. Proton nuclear magnetic resonance (1H NMR), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and oscillatory rheometry were performed, and it was confirmed that the reversibility of the HUB increases as the order of isocyanate group increases (1° > 2° > 3°). Self-healing behaviours were examined by single scratch tests, and the self-healing efficiency increased in the same order. Blending of two isocyanates, 1,4-bis(isocyanatomethyl)benzene (XDI) and tetramethylxylene diisocyanate (TMXDI), expanded the choices for the mechanical and self-healing properties of the polymers. It was remarkable that the mechanical properties of the HUB-bearing polymers at ambient temperature were more significantly affected by the spacer structure of diisocyanate than the steric hindrance.