L. J. S. Johnson

Bio: L. J. S. Johnson is an academic researcher from Sandvik Coromant. The author has contributed to research in topics: Coating & Cutting tool. The author has an hindex of 5, co-authored 16 publications receiving 77 citations. Previous affiliations of L. J. S. Johnson include Linköping University.

Strength, transformation toughening, and fracture dynamics of rocksalt-structure T i 1 − x A l x N ( 0 ≤ x ≤ 0.75 ) alloys

Abstract: Ab initio-calculated ideal strength and toughness describe the upper limits for mechanical properties attainable in real systems and can, therefore, be used in selection criteria for materials design. We employ density-functional ab initio molecular dynamics (AIMD) to investigate the mechanical properties of defect-free rocksalt-structure (B1) TiN and $\text{B}1\mathrm{T}{\mathrm{i}}_{1\ensuremath{-}x}\mathrm{A}{\mathrm{l}}_{x}\mathrm{N}\phantom{\rule{4pt}{0ex}}(x=0.25$, 0.5, 0.75) solid solutions subject to [001], [110], and [111] tensile deformation at room temperature. We determine the alloys' ideal strength and toughness, elastic responses, and ability to plastically deform up to fracture as a function of the Al content. Overall, TiN exhibits greater ideal moduli of resilience and tensile strengths than (Ti,Al)N solid solutions. Nevertheless, AIMD modeling shows that, irrespective of the strain direction, the binary compound systematically fractures by brittle cleavage at its yield point. The simulations also indicate that $\mathrm{T}{\mathrm{i}}_{0.5}\mathrm{A}{\mathrm{l}}_{0.5}\mathrm{N}$ and $\mathrm{T}{\mathrm{i}}_{0.25}\mathrm{A}{\mathrm{l}}_{0.75}\mathrm{N}$ solid solutions are inherently more resistant to fracture and possess much greater toughness than TiN due to the activation of local structural transformations (primarily of B1 \ensuremath{\rightarrow} wurtzite type) beyond the elastic-response regime. In sharp contrast, (Ti,Al)N alloys with 25% Al exhibit similar brittleness as TiN. The results of this work are examples of the limitations of elasticity-based criteria for prediction of strength, brittleness, ductility, and toughness in materials able to undergo phase transitions with loading. Comparing present and previous findings, we suggest a general principle for design of hard ceramic solid solutions that are thermodynamically inclined to dissipate extreme mechanical stresses via transformation toughening mechanisms.

Coated cutting tool for metal cutting applications generating high temperatures

Abstract: The present invention relates to a cutting tool insert comprising a body of cemented carbide, cermet, ceramics, high speed steel (HSS), poly crystalline diamond (PCD) or polycrystalline cubic boron nitride (PCBN), a hard and wear resistant coating is applied, grown by physical vapour deposition (PVD) such as cathodic arc evaporation or magnetron sputtering. Said coating comprises at least one layer of (Zr x Ali 1-x )N with of 0.45 < x < 0.85 and 0.90 < y < 1.30 with a thickness between 0.5 and 10 μm. Said layer has a nanocrystalline microstructure consisting of a single cubic phase or a mixture of hexagonal and cubic phases. The insert is particularly useful in metal cutting applications generating high temperatures with improved crater wear resistance.

Morphology and microstructure evolution of Ti-50 at.% Al cathodes during cathodic arc deposition of Ti-Al-N coatings

Abstract: Today's research on the cathodic arc deposition technique and coatings therefrom primarily focuses on the effects of, e.g., nitrogen partial pressure, growth temperature, and substrate bias. Detailed studies on the morphology and structure of the starting material—the cathode—during film growth and its influence on coating properties at different process conditions are rare. This work aims to study the evolution of the converted layer, its morphology, and microstructure, as a function of the cathode material grain size during deposition of Ti-Al-N coatings. The coatings were reactively grown in pure N2 discharges from powder metallurgically manufactured Ti-50 at.% Al cathodes with grain size distribution averages close to 1800, 100, 50, and 10 μm, respectively, and characterized with respect to microstructure, composition, and mechanical properties. The results indicate that for the cathode of 1800 μm grain size the disparity in the work function among parent phases plays a dominant role in the pronounced...

Influence of pulsed-substrate bias duty cycle on the microstructure and defects of cathodic arc-deposited Ti1-xAlxN coatings

Abstract: The influence of pulsed substrate bias duty cycle on the growth, microstructure, and defects of Ti1-xAlxN coatings grown by cathodic arc deposition was investigated. Ti1-xAlxN coatings of varying compositions (x = 0.56, 0.38, 0.23) were deposited on cemented carbide substrates with 10, 25, 50, and 95% duty cycles of −50 V pulsed-bias under 10 Pa of pure N2 gas. Coatings grown at low duty cycles (10 and 25%) showed strongly textured, under-dense coatings with facetted columns and low amount of lattice defects. Applying higher duty cycles (50 and 95%) produced coatings that have denser microstructures, less preferred orientation, increasing compressive stresses and increased lattice defect densities. Our study elucidates how duty cycle variation not only changes the overall average energy supplied at the growth front but also kinetically influences the coating growth and thus microstructure and defect structure.

Botulinum toxin A as an adjunct to treatment in the management of the upper limb in children with spastic cerebral palsy (UPDATE)

Abstract: Background Cerebral palsy (CP) is a central nervous system deficit resulting from a non-progressive lesion in the developing brain. Although the brain lesions are static, the movement disorders that arise are not unchanging and are characterised by atypical muscle tone, posture and movement (Rang 1990). The spastic motor type is the most common form of CP and its conventional therapeutic management may include splinting/casting, passive stretching, facilitation of posture and movement, spasticity-reducing medication and surgery. More recently, health care professionals have begun to use botulinum toxin A (BtA) as an adjunct to interventions in an attempt to reduce muscle tone and spasticity to improve function Objectives To assess the effectiveness of intramuscular BtA injections as an adjunct to managing the upper limb in children with spastic CP. Search strategy We searched the Cochrane Central Register of Controlled Trials (The Cochrane Library, Issue 4, 2003), MEDLINE (1966 to March Week 3 2004), EMBASE (1980 to 2003 Week 16) and CINAHL (1982 to Week 3 March 2004). Selection criteria All randomised controlled trials (RCTs) comparing intramuscular BtA injections into any muscle group of the upper limb with placebo, no treatment or other interventions. Data collection and analysis Two authors using standardised forms extracted the data independently. Each trial was assessed for internal validity with differences resolved by discussion. Data was extracted and entered into RevMan 4.2.3. Main results Two trials met the inclusion criteria, each having short-term follow up, a small number of subjects and using a single set of injections. The study by Corry 1997 compared BtA with an injection of normal saline and found promising results in elbow extension, elbow and wrist muscle tone. At three months, encouraging results for wrist muscle tone and grasp and release were noted. The trial reported median change, range of changes and the difference in these measures between groups. The study by Fehlings 2000 compared BtA with no intervention. When data were analysed no treatment effect was found for quality of upper limb function, passive range of motion, muscle tone, grip strength or self-care ability. Reviewers' conclusions This systematic review has not found sufficient evidence to support or refute the use of intramuscular injections of BtA as an adjunct to managing the upper limb in children with spastic cerebral palsy. Only one of the two identified RCTs reported some promising results in support of reduced muscle tone following BtA injections. Further research incorporating larger sample sizes, rigorous methodology, measurement of upper limb function and functional outcomes is essential.

A structure zone diagram including plasma based deposition and ion etching - eScholarship

Abstract: An extended structure zone diagram is proposed that includes energetic deposition, characterized by a large flux of ions typical for deposition by filtered cathodic arcs and high power impulse magnetron sputtering. The axes are comprised of a generalized homologous temperature, the normalized kinetic energy flux, and the net film thickness, which can be negative due to ion etching. It is stressed that the number of primary physical parameters affecting growth by far exceeds the number of available axes in such a diagram and therefore it can only provide an approximate and simplified illustration of the growth condition?structure relationships.

Effect of adhesion and the wear-resistant layer thickness ratio on mechanical and performance properties of ZrN - (Zr,Al,Si)N coatings

Abstract: The study involved the investigation of the effect of the thickness of the adhesion layers (0.3 and 0.7 μm) and the wear-resistant layer (2.0, 4.0, 6.0, and 8.0 μm) on the microhardness, adhesion bond strength, and performance properties of the ZrN-(Zr,Al,Si)N coatings. The scratch-test method was applied to study the adhesion bond strength to the substrate and coating failure patterns. The study revealed an effect of the coefficient kwa, determining the effect of the thicknesses of the wear-resistant and adhesion layers of the coating on the value of the critical load LC2. The study investigated the wear patterns and mechanisms for the specified coatings and the tool life of tools with these coatings in turning. An effect of the coefficient kwa which is the adhesion and wear-resistant layer thickness ratio on the tool life and a difference in the wear pattern dynamics for tools with these coatings with wear-resistant layers of equal thickness and adhesion layers of different thicknesses was revealed. The study also determined the chemical and phase composition of the coatings.

Surface modification of titanium alloy using hBN powder mixed dielectric through micro-electric discharge machining

Abstract: In the present study, hard, wear, and corrosion resistance coating is deposited on titanium alloy with hexagonal boron nitride powder (avg. size 70 nm) suspended in deionized water by micro-electro discharge coating process. The influence of input process parameters on surface integrity, wear properties, and corrosion resistance is studied. XRD analysis of coating surface shows the presence of phases such as BN, Al2O3, TiN, TiAlN, TiO, and CuO. Micro-hardness of the coating surface increases by five times as compared to titanium alloy (parent material). At the parameter settings of 60 V, 0.7 duty factor, and 12 g/l, the maximum deposition rate of 5.65 ± 0.1 × 10−4 g/min and recast layer thickness of 13.1 μm is obtained. Pin on disk wear test results reveal the reduction of wear rate of the coated surface to one-fourth of that of the base material. The average coefficient of friction (COF) for the deposited BN surfaces reduces to 0.26 from 0.4 (substrate material). Corrosion resistance of the coated surface is found to be 1.24 μm/year in flowing water conditions and 1.07 μm/year in stagnant water whereas for the parent material it is 5.92 μm/year in flowing water condition and 4.89 μm/year for stagnant water condition.