Diamond Grits Research Articles

Influence of cold plasma on material removal behavior during diamond grit scratching single crystal silicon

As a typical brittle crystal material, single crystal silicon has high hardness and brittleness, which makes the machined surface prone to microscopic cracks and other subsurface damage. In addition, the anisotropic crystal structure may cause large differences in the material removal behavior along different crystal orientations. To solve these problems, researchers have proposed the methods of machining along the easy-to-cut direction and inducing external energy fields assisted machining, but there remain problems like cracks and surface thermal damage. In this study, we propose to modulate the deformation process of single crystal silicon by atmospheric pressure cold plasma and elucidate the influence of plasma on the material removal behavior based on diamond grit scratching experiments along different directions. The results show that before plasma treatment, the toughness along <110> direction is higher than that along <100> direction, and plasma has significant improvement effects on the plastic deformability in both directions. The critical load for plastic-brittle transition along <110> direction can be increased from 76.2 mN to 107.1 mN, and from 69.6 mN to 109.8 mN along <100> direction. The plasticity regulation mechanism is that the interaction of multiple shear bands dissipates the energy of crack propagation and inhibits the premature generation of cracks. Compared with the conventional scratching along <110> direction, the material removal rate of plasma-assisted scratching under normal loads of 20 mN, 40 mN and 80 mN can be increased by 30.2%, 24.2% and 21.9%, respectively; while that along <100> direction can also be increased by 33.7% and 19.5% under 20 mN and 40 mN, respectively. This study may provide a novel approach for realizing high-quality and efficient processing of hard and brittle materials.

Cutting efficiency of different dental diamond rotary instruments for sectioning monolithic zirconia and lithium disilicate crowns

BackgroundThe aim of this study was to determine the cutting efficiency of different diamond rotary instrument types for sectioning monolithic zirconia and lithium disilicate anatomical crowns.Materials and methodsThe study used 30 diamond rotary instruments divided into three groups: Zirconia cutting diamond bur (White Z), super coarse grit diamond bur (KBlack), and medium coarse grit diamond bur (KBlue); Two subgroups were assigned based on the crown materials including monolithic zirconia (5YSZ) and lithium disilicate (e.max) ceramics. The cutting efficiency was assessed by measuring the time required to fully section the crowns, followed by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) of the dental burs before use and after every sectioned crown. A three-way ANOVA examined the effects of bur type, material type, and sectioning stage. If interaction exists, one-way ANOVA was used to compare the different subgroups, followed by the Tukey post hoc test. The significance level was assigned at α ≤ 0.05.ResultsThe results exhibited various cutting efficiencies among diamond rotary instruments and ceramic crown materials. White Z demonstrated superior cutting efficiency of zirconia crown compared with KBlack and KBlue for the first cutting cycles (p ≤ 0.05); the results tend to be more comparable at the third cutting cycle. However, the super coarse diamond bur exhibited higher efficiency in cutting lithium disilicate crowns than white Z and KBlue burs through all three cutting cycles(p ≤ 0.05). The diamond bur-cutting efficiency diminished after each use, irrespective of the bur type or the crown material (p ≤ 0.05); this was represented by the reduction of carbon and increased nickel matrix ratio after each bur usage.ConclusionWhite Z diamond bur showed higher cutting efficiency of zirconia in the first two cutting cycles; super coarse diamond bur is more efficient for cutting lithium disilicate crown in all of the cutting cycles. The amount of diamond on the burs reduced after each use, with no great impact on the material type when sectioning lithium disilicate and 5YSZ crowns.Clinical significanceThis study provides valuable insights for dental practitioners in selecting the appropriate diamond rotary instrument for crown sectioning. Practitioners can minimize the risk of damage and reduce the time required for crown removal, improving patient outcomes.

The effect of surface treatment and thermal aging on the bonding of clear aligner attachments to provisional resin-based material: shear bond strength analysis.

The aim of this study is to evaluate the effect of different surface treatments on the shear bond strength (SBS) of clear aligner attachments bonded to Bis-acryl provisional crowns. 120 cylindrical bisacrylic composite material (ProTemp type) specimens were prepared and divided into six groups (n = 20) based on surface treatment, control: (no treatment); super coarse grit diamond bur, carbide bur, alumina-blasting, non-thermal plasma treatment, and Er:YAG laser treatment. The features of treated surfaces were examined using scanning electron microscopy (SEM). A flowable composite resin (Transbond XT; 3M Unitek) was bonded to the specimens forming the attachment. Half of specimens were subjected to thermal cycling (5,000 cycles). SBS was measured before and after thermal cycling. Each specimen was loaded at the attachment/resin interface at a speed of 0.5 mm/min until failure. The nature of the failure was analyzed using the composite remnants index (CRI). Two-way ANOVA and Tukey HSD were used for data analysis α = 0.5. For CRI scores analysis, Kruskal-Wallis test and Dunn's multiple comparison were used as post-hoc test. SEM analysis showed that all surface treatments altered surface properties and increase surface bonding area. The specimens treated with plasma, Er:YAG laser, and alumina-blasting had higher SBS values before and after thermal cycling. In comparison to control plasma, Er:YAG laser, and alumina-blasting showed a significant increase in SBS (P < 0.001) while carbide and diamond bur groups showed no significant differences (P > 0.05). Thermal cycling significantly decreased the SBS of control, carbide bur, diamond bur, and Er:YAG laser while no significant effect of alumina-blasting and plasma group. Er:YAG laser and plasma groups significantly exhibited more dominance for scores 2 and score 3 and the absence of score 0. Alumina-blasting, Er:YAG laser, or non-thermal plasma surface treatments increased the shear bond strength between clear aligner attachments and resin-based restorations.

Influence of grit friability and grit distribution pattern on dry grindability of WC-6Co by single layered brazed diamond wheels

Single-layered brazed diamond wheels, composed of uni-layered diamond grits, metal binder, and metal core, have potentially good thermal conductivity to dissipate heat from the grinding zone. Considering this characteristic feature, the current study aims to explore the performance and suitability of various indigenously developed single-layered brazed diamond tools in plunge-grinding of fine-grained cemented carbide in a challenging dry atmospheric condition. Single crystalline synthetic diamond particles with different strengths and friability were utilized to develop indigenous diamond wheels with random and patterned grit distribution. The current study explores the role of diamond-grit friability and grit distribution patterns to identify the most suitable wheel for dry grinding of WC-6Co composite. Detailed analysis of the wheel morphology, signifying the fracture behavior of the diamond grit used, justified the variation in the grinding forces, tool life, and ground surface roughness. Irrespective of the grit and distribution type, all wheels showed saturation of dynamic changes in work-surface topography with the number of passes and more sensitively to the degree of increase of uncut chip thickness. Grinding wheels containing friable diamond grits with irregular granular structures performed better than the high-strength, cubo-octahedral grains during the dry grinding experiments.

Enhancement of the Refractory Matrix Diamond-Reinforced Cutting Tool Composite with Zirconia Nano-Additive.

This paper presents the results of the experimental research on diamond-reinforced composites with WC-Co matrices enhanced with a ZrO2 additive. The samples were prepared using a modified spark plasma sintering method with a directly applied alternating current. The structure and performance of the basic composite 94 wt.%WC-6 wt.%Co was compared with the ones with ZrO2 added in proportions up to 10 wt.%. It was demonstrated that an increase in zirconia content contributed to the intense refinement of the phase components. The composite 25 wt.%Cdiamond-70.5 wt.%WC-4.5 wt.%Co consisted of a hexagonal WC phase with lattice parameters a = 0.2906 nm and c = 0.2837 nm, a cubic phase (a = 1.1112 nm), hexagonal graphite phase (a = 0.2464 nm, c = 0.6711 nm), as well as diamond grits. After the addition of zirconia nanopowder, the sintered composite contained structural WC and Co3W3C phases, amorphous carbon, tetragonal phase t-ZrO2 (a = 0.36019 nm, c = 0.5174 nm), and diamond grits-these structural changes, after an addition of 6 wt.% ZrO2 contributed to an increase in the fracture toughness by more than 20%, up to KIc = 16.9 ± 0.76 MPa·m0.5, with a negligible decrease in the hardness. Moreover, the composite exhibited an alteration of the destruction mechanism after the addition of zirconia, as well as enhanced forces holding the diamond grits in the matrix.

Material Removal Mechanism of SiC Ceramic by Porous Diamond Grinding Wheel Using Discrete Element Simulation.

SiC ceramics are typically hard and brittle materials. Serious surface/subsurface damage occurs during the grinding process due to the poor self-sharpening ability of monocrystalline diamond grits. Nevertheless, recent findings have demonstrated that porous diamond grits can achieve high-efficiency and low-damage machining. However, research on the removal mechanism of porous diamond grit while grinding SiC ceramic materials is still in the bottleneck stage. A discrete element simulation model of the porous diamond grit while grinding SiC ceramics was established to optimize the grinding parameters (e.g., grinding wheel speed, undeformed chip thickness) and pore parameters (e.g., cutting edge density) of the porous diamond grit. The influence of these above parameters on the removal and damage of SiC ceramics was explored from a microscopic perspective, comparing with monocrystalline diamond grit. The results show that porous diamond grits cause less damage to SiC ceramics and have better grinding performance than monocrystalline diamond grits. In addition, the optimal cutting edge density and undeformed chip thickness should be controlled at 1-3 and 1-2 um, respectively, and the grinding wheel speed should be greater than 80 m/s. The research results lay a scientific foundation for the efficient and low-damage grinding of hard and brittle materials represented by SiC ceramics, exhibiting theoretical significance and practical value.

Non-linear diamond material removal at increased sliding velocities in ultra-precision grinding

Single crystal diamond machining primarily relies on mechanical grinding, traditionally guided by the simplistic concept of a linear removal rate. However, this conventional approach lacks precision in predicting the resultant shape. This comprehensive study delves into the influence of sliding speed on the material removal rate during the mechanical grinding of diamond, leveraging both theoretical frameworks and experimental exploration. Initially, the impact of sliding velocity is meticulously scrutinized by considering the contact frequency between the diamond and grinding wheel grits, as well as the depth associated with the brittle-ductile transition of diamond material. Subsequently, a model quantifying the effect of sliding velocity is meticulously formulated and rigorously tested through experimentation. The findings of this investigation not only affirm the validity of the theoretical analyses but also underscore the remarkable predictive accuracy of the sliding velocity effect model. These results, situated at the intersection of theory and practice, offer invaluable insights with profound implications for enhancing the efficiency and precision of single crystal diamond machining processes.

Study on the material removal mechanism and the exit breakage of ultrasonic vibration-assisted grinding for microcrystalline glass

With the aim of solving problems such as exit breakage and surface microcracks during microcrystalline glass machining, an ellipsoidal erosion model is established by analyzing the motion trajectory and characteristics of single diamond grit in ultrasonic vibration-assisted grinding (UVAG), and the material removal volume of single diamond grit particles is obtained. A simulation model of UVAG of microcrystalline glass is established by the finite element method. The effect of process parameters such as rotational speed, grinding depth, feed rate on grinding force and workpiece edge stress has been investigated. The experiment of UVAG for microcrystalline glass is performed on a five-axis CNC machine with the same process parameters, and the surface morphology, surface roughness, and exit breakage sizes of microcrystalline glass are observed. The results show that with the increase in grinding depth, the average grinding force between the tool and the workpiece increases, and the proportion of material removal in a brittle fracture increases. As the rotational speed increases, the grinding force between the tool and the workpiece gradually decreases and results in an improvement in the surface quality of the workpiece. As the feed rate increases, the surface roughness increases by 16.76%, the width of the edge breakage increases by 109.19%, and the thickness of the edge breakage increases by 104.49%.

Study of side burr formation in steady-state nano-polishing of Si-wafer using molecular dynamics simulation

With advancements in the semiconductor industry, it is required to have angstrom level surface finish on silicon wafers which is achieved by nano-polishing. However, side burr is formed due to material pile-up from material removal due to abrasive which becomes detrimental to achieving the high surface finish. This study employs molecular dynamics simulations to explore the mechanism underlying side burr formation during nano-polishing of mono-crystalline silicon (Si)-wafer. The study utilizes a diamond nano-abrasive grit to scratch the surface of the Si-wafer and investigates the formation of pile-ups during the steady-state process. It was observed that increasing the depth of cut by four times led to a 6.3-fold increase in the number of amorphous atoms, indicating greater bond breakage in the direction of scratching. As a result, the cutting force exceeds the thrust force at larger depths of the cut. The correlation between the side burr height and the depth of cut is also studied. Results show that the side burr height ratio increases with the depth of cut, indicating a higher sensitivity of side burr height to the depth of cut. The study suggests that to achieve a ductile mode of material removal and minimize the height of the side burr during nano-polishing of Si-wafers, it is crucial to maintain the depth of cut at or below half (≤0.5) of the abrasive radius and ensure an average friction coefficient below 0.6. The outcome of this study can be useful for the actual manufacturing of miniaturized sensors, actuators, and microsystems for microelectromechanical system devices where a high surface finish is crucial.

Magnetization and self-sharpening mechanism of polymerized diamond abrasive based on magnetorheological polishing technology

In magnetorheological polishing (MRP), the abrasive grains are confined in a semi-fixed mode by the chain strings formed by the magnetorheological particles to achieve the polishing of workpiece surfaces. The force of the abrasive particles on the workpiece comes from the force of the magnetic chain strings acting on the abrasives. However, the angular surface of the abrasive is generally smooth, resulting in a limited holding force on the abrasive by the magnetic chain strings. Therefore, the polishing force of the abrasives on the workpiece is small, and it is easy to slip and escape from the polishing area. In this paper, the sintering method is used to prepare polymerized diamond abrasive(PD) with microstructures on the surface, to increase the surface area of the abrasive and to improve the control force of the magnetic chain string on the abrasive. The prepared PD has a particle size of about 25.7 μm, with a rough surface and a large amount of 3 μm single-crystal diamond particles exposed. The MRP results show that the PD have more surface micro-cutting edges and stronger machinability than the commonly used single-crystal diamond abrasives(SCD). The material removal rate(MRR) of PD on silicon wafers and sapphire wafers was increased by 173.3 % and 122.2 %, respectively. The morphological changes of the PD were traced by scanning electron microscope(SEM), and it was found that: when polishing low-hardness materials, the wear of the PD was in the form of ceramic bond wear and diamond grit dislodgement; and when polishing high-hardness materials, the wear of the PD was in the form of ceramic bond breakage and PD fragmentation. When abrasive grit dislodgment occurs on the surface of the PD, the formed hole enhances the force between the PD and the magnetic chain strings. Which further enhances the holding force of the magnetic chain string on the PD, and can effectively improve the magnetorheological polishing efficiency.

Ultra-precision lapping of H2O(g) plasma-treated CaF2 by porous diamond grits

The calcium fluoride (CaF2) component has excellent light transmission and a high laser damage threshold in the UV band, and thus is a potentially ideal material for high-power laser facility. However, the low-damage surface is difficult to attain via the existing processing technologies due to its brittleness, especially the dissociation property of the (111) surface. We innovatively propose H2O(g) plasma-assisted porous diamond abrasive lapping technology to achieve low-damage and high-precision surface processing of CaF2 component, which means that the CaF2 component is modified first and then the softened modified layer is removed by the porous diamond abrasive lapping. The H2O(g) plasma modification mechanism was elucidated through a combination of molecular dynamics simulation and experiment and comparison with H2O(g) plasma etching. The modification layer including an oxide layer and a phase change layer was produced by adjusting the plasma processing process (power of 25 W and H2O(g) content of 10 ml). Then the modified CaF2 component was lapped by the porous diamond abrasive tool on the ductile domain layer which is more than the modified layer and less than the sum of the modified layer and plastic domain. When the lapping process parameters were 200 rpm platen rotation speed and 20 N lapping pressure, a surface accuracy of 15.34 nm PV, 2.29 nm RMS (φ1 mm) was obtained. This study provides technical support for the low-damage processing of CaF2 component.

Synthesis and lapping performance of a detonation nanodiamonds slurry by a SPS deagglomeration technology

In order to obtain a simple and efficient technique to prepare detonation nanodiamonds (DNDs) lapping slurry, deagglomerate DND powders by a spark plasma sintering (SPS) technology was proposed in the present study. The effect of SPS treatment temperature on the surface characteristics and dispersion properties of DND powders in deionized water have been studied. The best deagglomeration of DND powders with the peak particle size distribution of 79 nm is achieved for the DND that treated by SPS at 500 °C. The DND dispersed water solution is used as lapping slurry for the four ceramics (Al2O3, AlN, Si3N4, and 3Y-TZP) with different mechanical properties. The material removal rate and surface quality of the four ceramics in lapping process were also examined and compared, in which showed the highest material removal rate for 3Y-TZP and the lowest for Si3N4. The surface roughness of the four ceramics can be decreased to <10 nm by lapping sequentially with slurry of diamond grit size of 3, 0.5, and 0.1 μm and DND slurries successively. Compare to Al2O3 and AlN, 3Y-TZP and Si3N4 ceramics show lower surface roughness. And a lowest roughness of Ra 3.4 nm is achieved for 3Y-TZP. In lapping of AlN ceramic, Al(OH)3 is formed due to the hydrolysis reaction, which is produced shallow pits with the size of grain.

An analytical dynamic force model for sawing force prediction considering the material removal mode

Diamond circular saw blades are indispensable tools in the industry of granite processing. Accurate prediction of sawing force is essential for optimizing the processing in advance. In this study, the calculation method for uncut chip thickness and instantaneous chip thickness was improved based on granite sawing characteristics. Furthermore, an analytical prediction force model was proposed in view of deep and intermittent grinding, which comprehensively considers the characteristics of diamond grits (including grit size, location distribution, and protrusion height) and material removal mode. The error between the predicted results and the experimental results is <12 %, indicating that the model can accurately predict the cutting force. The proposed analytical model provides a method to optimize the sawing parameters without the need for extensive experiments. This model can also extend to calculate parameters such as energy consumption and carbon emissions in the stone processing industry.

Improvement in Abrasive Wear Resistance of Metal Matrix Composites Used for Diamond-Impregnated Tools by Heat Treatment.

This work presents the possibilities of producing a substitute for a commercial matrix material for sintered metal-diamond tools which is characterized by increased tribological properties required in machining natural stones and concrete. In this study, the improvement in wear behavior of sintered pre-alloyed matrix caused by a thermal treatment was investigated. Several mixtures made of commercially available powders were homogenized by ball milling and consolidated at 900 °C using the spark plasma sintering (SPS) method. During cooling down, the specimens were subjected to isothermal holding at 350 or 250 °C for 1 h. After consolidation, all specimens were tested for density and hardness, whereas selected specimens were characterized by scanning electron microscopy (SEM) and flexural strength tests. The specimens made of BDCM50 powder (a mixture of the base and pre-alloyed powders in 50:50 proportion) shows excellent properties including σ0.2 = 1045 MPa in the three-point bending test and HV10 ≈ 380. Resistance to abrasive wear evaluated in both three-body and two-body conditions in the MWT abrasion test was estimated at Ai3=18.1±3.9 μm/20 m and Ai2=95.9±11.8 μm/20 m, respectively. A series of diamond-impregnated specimens (segments) was also produced and tested for wear rate on abrasive concrete. The potential graphitization of the diamond grits was investigated using Raman spectroscopy and X-ray diffraction. As a reference, both the base Fe-Mn-Cu-Sn-C and commercially available Co+20%WC alloy were used to compare selected properties of the investigated materials. It has been proved that heat-treated specimens made of the base mixture modified with pre-alloyed powders are characterized by increased hardness and resistance to abrasive wear. The BDCM50 matrix has a negligible effect on diamond graphitization and shows excellent field performance, which makes it a good potential substitute for replacing Co+20%WC in sintered diamond-impregnated tools.

Evaluating the performance of electrical discharge face grinding on super alloy monel 400

Conventional machining of super alloy Monel 400 is difficult due to its high strength, low heat conductivity, and gummy nature. In this work, the performance of the electrical discharge diamond face grinding (EDDFG) while processing supper alloy Monel 400 is assessed using the super abrasive diamond-coated grinding wheels of three different grit numbers. Preliminary experiments highlighted the superior performance of the EDDFG as compared to that of electrical discharge machining (EDM) and electrical discharge face grinding (EDFG); in terms of material removal rate (MRR), average surface roughness (Ra), and microscopic images of surfaces using scanning electron microscope (SEM). This work aimed to assess the influence of the diamond grit number (DG n ) of the grinding wheel along with other process parameters, viz. grinding wheel speed (GWS), peak current (I p ), and pulse-on-time (T on ) on Ra and MRR. The analysis of variance (ANOVA) confirmed that DG n and GWS significantly affect the response variables. Finally, the multi-objective genetic algorithm (GA) optimization approach was used to determine the optimal parametric settings of the EDDFG process.

The effect of temperature and dwell time on diamond-WC brazed joint quality using low-melting point active Ag-Cu-In alloy

The recent demand for developing micro-pin Diamond grinding tools has gained tremendous importance in tool manufacturing industries. A successful development of these tools requires joining Diamond grits to carbide surface firmly. In this context, the present paper demonstrates the joining of Diamond grits to WC-cermet surface via brazing route using Ag-Cu-24.3In-3Ti active alloy (Incusil-ABA). All brazing experiments were conducted using a resistance type heating furnace under a highly controlled vacuum environment to eliminate contamination. Experimental findings of this investigation indicate that both brazing temperature and dwell time have significant influence on microstructure and other related properties of the alloy. Titanium present in the alloy was found to segregate towards Diamond-alloy interface. It was expected that such segregation would ensure a proper wetting by the alloy. However, the overall morphology of the brazed joint revealed that improper melting and poor wetting by alloy on cermet surface were two major challenges. The current study showcases that a careful control on brazing temperature and dwell time demonstrates a remarkable improvement in wetting characteristics and alloy morphology. It has been observed that a brazing temperature of 780 °C and dwell time of 15 min resulted in a good brazed joint morphology. The study also investigated the effect of said brazing temperature on grits physical characteristics using Raman spectroscopy. At the end, scratch test and wear characteristics of the filler are investigated in detail. The outcome of this investigation will be of immense interest to tool manufacturing industries associated with development of brazed micro-pin Diamond grinding tools using alloys having low melting point.

Influence of different surface treatment on bonding of metal and ceramic Orthodontic Brackets to CAD-CAM all ceramic materials

BackgroundDeveloping efficient bonding techniques for orthodontic brackets and all-ceramic materials continues to pose a clinical difficulty. This study aimed to evaluate the shear bond strengths (SBS) of metal and ceramic brackets to various all-ceramic CAD-CAM materials, such as lithium disilicate CAD (LDS-CAD), polymer-infiltrated ceramic (PIC), zirconia-reinforced lithium silicate glass ceramic (ZLS), and 5YTZP zirconia after different surface treatments and thermal cycling.Materials and methodsThe samples were divided into two groups to be bonded with ceramic and metal lower incisor brackets. Each group was subdivided into a control group devoid of any surface treatment, 10% HF acid (HFA) etching, ceramic etch & prime (MEP), Al2O3 air abrasion, and medium grit diamond bur roughening. After surface treatment, brackets were bonded with composite resin cement, thermal cycled, and tested for shear bond strength. The failed surfaces were evaluated with a digital microscope to analyse the type of failure. The data were statistically analysed using a one-way ANOVA and Tukey HSD tests at p < 0.05.ResultsThe highest mean bond strengths were found with HFA etching in LDS-CAD (13.17 ± 0.26 MPa) and ZLS (12.85 0.52 MPa). Diamond bur recorded the lowest mean bond strength roughening across all the ceramic groups. There were significant differences in mean shear bond values per surface treatment (p < 0.001) and ceramic materials.ConclusionAmong the surface treatment protocols evaluated, HFA etching and MEP surface treatment resulted in enhanced bond strength of both ceramic and metal brackets to CAD-CAM all ceramic materials.

Wear evolution of metal bond diamond tool in grinding of sapphire

The wear characteristics of the metal bond diamond tools changes with the grinding process, resulting in affecting the grinding efficiency, tool's life, and surface integrity of the workpiece. In this study, the wear evolution of a metal bond diamond tool, for the case of grinding of sapphire, is investigated by using a novel design of the grinding setup. The wear characteristics of the diamond grits and the metal bond at a fixed zone of the grinding tool were examined. In addition, the evolution of the grinding process, the grinding force, the grinding ratio, and the surface integrity of the sapphire were also evaluated. As the material removal volume increases, the number of participating diamond grits, the proportion of micro-fractured diamond grits, and the average diamond grit protrusion height increase during the grinding process. And the proportion of newly exposed diamond grits decreases and the distribution of protrusion height of diamond grits becomes narrower during the grinding process. Consequently, a higher grinding ratio, stable grinding force, and excellent ground surface integrity are achieved positively when the wear of the metal bond diamond tool transforms from the initial stage to the stable stage with the material removal volume of up to 3600 mm3.

Strengthening Mechanisms and Retention Properties of Sintered Iron-Based Matrix Material for Metallic-Diamond Tools.

This work presents the analysis of mechanisms controlling the deformation strengthening of the surface during abrasion and their impact on structural changes and mechanical properties of Fe-Mn-Cu-Sn-C matrix material, which was prepared by means of powder metallurgy (PM). The powder mixture was ball-milled for 8 h and densified to <1% porosity using hot pressing at 900 °C and 35 MPa. Phases and structural transformations taking place in austenite during plastic deformation were identified. The participation, distribution, and morphology of the phases, as well as the physicomechanical properties of the matrix material, were tested. It has been shown that during grinding, deformation twins are generated in areas where an austenitic microstructure is present. To test the ability of the matrix to keep diamond crystals firmly cylindrical (Ø11.3 mm× 5 mm), diamond-impregnated specimens containing diamond grits of 30/40 mesh in size and at a concentration of 20 (5% vol.) were prepared. It was finally determined by the diamond-retention index, which is the number of retained diamond particles compared to the total number of diamond particles and the pullouts on the working surface of the segment. This research shows that materials containing Ti- and Si-coated diamond particles, deposited by the CVD method, have the highest abrasion resistance and, therefore, have the best retention properties. In order to determine the bonding mechanism at the matrix-diamond interface, specimens were also analyzed by SEM and TEM.

Microstructure and properties of brazed diamond with Pr-modified Ni[sbnd]Cr filler metals

The aim of this study is to improve the mechanical properties of diamond tools by brazing diamonds with a modified NiCr filler alloy to achieve the reduction of thermal damage. In this paper, rare earth Pr doping into NiCr filler alloy is brazed at 1080 °C under vacuum and tested for organization and properties. The results show that the doping of Pr refines the grain size and carbide. Moreover, Cr7C3 and Cr3C2 are generated at the brazed interface, which realizes the chemical metallurgical bonding and improves the bonding strength of the diamond. The generation of the NiPr phase reduces the thermal damage of brazed diamonds. When the addition of Pr is 1 wt%, the diamond grits have a more complete morphology. The exposed height reaches 46.6 % of its own height and the carbonized layer is thinner. The thermal damage is reduced. In addition, the frictional wear experiments and strength tests also shows that the performance of this filler alloy brazed diamond is better than the unmodified filler alloy brazed diamond.