Theoretical Insight Into Diamond Doping and Its Possible Effect on Diamond Tool Wear During Cutting of Steel

Natural diamond tools experience wear during cutting of steel. As reported in our previous work, Ga doping of diamond has an effect on suppressing graphitization of diamond which is a major route of wear. We investigate interstitial and substitutional dopants of different valence and different ionic radii (Ga, B, and He) to achieve a deeper understanding of inhibiting graphitization. In this study, ab initio calculations are used to explore the effects of three dopants that might affect the diamond wear. We consider mechanical effects via possible solution strengthening and electronic effects via dopant-induced modifications of the electronic structure. We find that the bulk modulus difference between pristine and doped diamond is clearly related to strain energies. Furthermore, boron doping makes the resulting graphite with stable sp2 hybridization more perfect than diamond, but Ga-doped diamond needs 2.49 eV to form the two graphene-like layers than only one layer, which would result in the suppressed graphitization and reduced chemical wear of the diamond tool.

Dynamic mechanical and thermal properties of clear aligners after thermoforming and aging

Background Based on the role of properties of aligner materials on their efficiency, we aimed to assess their thermomechanical properties after thermoforming and simulated aging. Methods In this experimental study, 96 samples of polyethylene terephthalate glycol (PETG) aligners (Duran and Erkodur) were prepared and divided to three groups: control (C), after thermoforming (T), after thermoforming and aging (TA). Thermoforming was done through 3D-printed molds, and aging was exerted by 200 thermal cycles after immersion in 37°C distilled water for 24h. Flexural modulus, hardness, glass transition temperature (Tg), elastic and viscous modulus, and loss factor were evaluated. Two-way ANOVA, T-independent, and Tukey HSD tests were done for statistical analysis and significance level was set to 0.05. Results In both materials, flexural modulus decreased significantly after thermoforming, 88% in Duran and 70% in Erkodur, but did not change significantly after aging. After thermoforming, hardness decreased significantly in both materials (22% in Duran and 7.6% in Erkodur). Dynamic Tg was significantly lower in T and TA in both materials. At all temperatures (25, 37, 55°C) in Duran, the elastic modulus difference was only significant between C and TA, but in Erkodur, it decreased significantly in T, and there was no significant change after aging. Viscous modulus and loss factor showed the same change patterns at all temperatures. In both materials, they increased after thermoforming, but did not change significantly after aging. Conclusion Thermoforming had more prominent role than aging in diminishing of thermomechanical properties. In general, Duran had greater thermomechanical stability than Erkodur.

Some Results on 2-odd Labeling of Graphs

A graph is said to be a 2-odd graph if the vertices of can be labelled with integers (necessarily distinct) such that for any two vertices which are adjacent, then the modulus difference of their labels is either an odd integer or exactly 2. In this paper, we investigate 2-odd labeling of some classes of graphs.

A Study on the Hall–Petch Relationship and Grain Growth Kinetics in FCC-Structured High/Medium Entropy Alloys

The recrystallization behavior, grain growth kinetics, and corresponding hardness variation of homogenized and 80% cold-rolled FeCoNiCrPd, FeCoNiCrMn, and their quaternary/ternary FCC-structured high/medium entropy alloys (H/MEAs) annealed under different conditions were investigated. Experimental results indicate that the grain size and hardness of these H/MEAs follow the Hall–Petch equation, with the Hall–Petch coefficient KH value being mainly dominated by the alloy’s stacking fault energy and shear modulus. The FeCoNiCrPd alloy exhibits the highest hardness of the H/MEAs at the same grain size due to the largest Young’s modulus difference between Cr and Pd. The grain growth exponent n, kinetic constant k, and activation energy for grain growth QG of all H/MEAs are calculated. The k can be expressed by the Arrhenius equation with QG, which is attributed to the diffusion rate. The results demonstrate that the QG values of these H/MEAs are much higher than those of conventional alloys; most notable is FeCoNiCrPd HEA, which has an unusually lattice distortion effect that hinders grain growth.

Dynamic Instability of Two Elastic Half-Spaces Sliding With a Rate-and-State Friction Constitutive Law

The destabilization of the steady-state regime of two semi-infinite half-spaces of different elastic coefficients sliding upon each other has been theoretically investigated when a rate-and-state friction constitutive law controls the sliding. In the framework of linear and isotropic elastodynamics, the effect of the frictional constitutive law has been investigated onto the development of self-excited oscillations as well as the influence of the shear modulus difference between the two materials. The possibility of existence of a stick–slip regime and the conditions for the loss-of-contact are finally discussed.

Optimization of Monitoring Points’ Layout for the Multi-Fan and Multi-Station Ventilation System

For optimal management and automatic supervision of the multi-fan and multi-station mine ventilation system, a certain number of monitoring points should be allocated in proper sites so as to provide necessary information reflecting the system’s operation status, which is an important part of on-line optimization management. The monitoring points’ setting is related to its number, location and network decomposition method. It’ll complicate the issue if taking the three factors into consideration all together. Divide the issue into 2 parts. First, use Fibonacci method to determine the monitoring points’ number without considering the location and network decomposition method. Second, determine the optimal location, and then get the optimal decomposition and maximum modulus difference. The application indicates it makes the problem easier to solve without much calculation.

Microstructure, Interface and Hardness of Ti/TiN Nanolayered Coatings

The polycrystalline Ti/TiN multilayer films were deposited by magnetron sputtering. We investigated the effects of mixed discharge gas pressure, bias voltage and substrate temperature on the microstructural, interfacial, and mechanical properties of the polycrystalline Ti/TiN multilayer films. X-ray reflectivity and diffraction (XRR and XRD), and nanoindentation were used to characterize the structures and mechanical properties for the films.The period of multilayer, interface width and grain size decrease with increaseing of deposition pressure. The multilayer coating at floating voltage shows TiN (111), Ti2N (103), and TiN (200) preferred crystalline orientation, whlie those at other different substrate biases show only TiN (111) and Ti2N (103) preferred crystalline orientation. It was found that the hardness increased with increasing substrate temperature. This hardness enhancement was probably caused by the modulus difference in the interface between layer Ti and TiN or the preferred crystalline orientation TiN(111).

Improvement of Tribological Behavior of Biomedical Nanostructured Titanium by Magnetron Sputtered SiC Films

The nano-indentation and friction/wear properties of a magnetron sputtered SiC (silicon carbon) films on nanostructured titanium (produced by severe plastic deformation) substrate were investigated. The results show that the films exhibited low nano-hardness (10.6 GPa), low Young's modulus (83.3 GPa) and high hardness-to-modulus ratio (0.128). As sliding against Si3N4 (silicon nitride) balls (2 mm in radius) under Kokubo simulation body fluid (SBF) at room temperature, the films displayed superior friction/wear properties at the considerably high normal load of 1000g, with the friction coefficient of about 0.18, the special wear rate on the order of 10−6 mm3 N-1m-1 without film cracking and interface delaminating. The impressive film cracking and interface delaminating resistance is in accordance with the low hardness (high ductility) of the films and the small film-substrate modulus difference that was caused by the low modulus of the films.

Evolution of Nanoindentation Hardness of Fe/Cu Nanometer-Scale Multilayers by Magnetron Sputtering

Fe/Cu nanometer-scale multilayers with nominal modulation wavelengths ranging from 5 to 40 nm are deposited by direct current magnetron sputtering on Si (100) substrates. Modulation structures of the multilayers are examined by small angle / wide angle x-ray diffraction (SA/WAXRD) and cross-sectional transmission electron microscopy (XTEM). Hardness of the multilayers is measured by using nanoindentation. All the multilayers have Fe (110) and Cu (111) textures. Interface coherency is observed in the multilayers with designed modulation wavelengths of 5 and 10 nm. The hardness increases firstly and then deceases with increasing the modulation wavelength, and reaches peak value of 7.29±0.29 GPa in the multilayers with nominal modulation wavelength of 10 nm. The evolution of the hardness of the mulitlayers is explained by interface width and modulus difference between sublayers.

The Near-Tip Stress Intensity Factor for a Crack Partially Penetrating an Inclusion

When a crack is lodged in an inclusion, the difference between the elastic modulus of the inclusion and matrix material will cause the near-tip stress intensity factor to be greater or less than that prevailing in a homogeneous material. A method is derived for calculation of the near-tip stress intensity factor for the inclusion with arbitrary shape. The derivation of the fundamental formula is based on the transformation toughening theory. The equivalent transformation strain contributed from modulus difference between inclusion and matrix is calculated from Eshelby equivalent inclusion approach. As validated by numerical examples, the developed formula has excellent accuracy.