Effect of phase transition on the unusual microwear behavior of superelastic niti sma

This paper focuses on the microwear behavior of NiTi and it is organized as follows. In section 2, the materials and testing methods are described. In section 3, the temperature dependent constitutive relations of the material during loading which involves both stress-induced phase transition and plasticity are first characterized. Detailed experimental results for the wear performance and hardness of the material measured at different temperatures are reported. The observations are analyzed in terms of the intrinsic temperature dependent constitutive law of the material, where the role of phase transition and its interaction with plasticity in the observed unusual wear performance is emphasized. The results are farther quantified in a simple contact model for indentation and wear. The final conclusions are given in section 4

Nanofretting behaviors of NiTi shape memory alloy

Nanofretting refers to cyclic movements of contact interfaces with the relative displacement amplitude at the nanometer scale, where the contact area and normal load are usually much smaller than those in fretting. Nanofretting widely exists in microelctromechanical systems (MEMS) and may become a key tribological concern besides microwear and adhesion. With a triboindenter, the nanofretting behaviors of a nickel titanium (NiTi) shape memory alloy are studied under various normal loads (1&ndash;10 mN) and tangential displacement amplitudes (2&ndash;500 nm) by using a spherical diamond tip. Similar to fretting, the nanofretting of NiTi/diamond pair can also be divided into different regimes upon various shapes of tangential force&ndash;displacement curves. The dependence of nanofretting regime on the normal load and the displacement amplitude can be summarized in a running condition nanofretting map. However, due to the surface and size effects, nanofretting operates at some different conditions, such as improved mechanical properties of materials at the nanometer scale, small apparent contact area and single-asperity contact behavior. Consequently, different from fretting, nanofretting was found to exhibit several unique behaviors: (i) the maximum tangential force in one cycle is almost unchanged during a nanofretting test, which is different from a fretting test where the maximum tangential force increases rapidly in the first dozens of cycles; (ii) the tangential stiffness in nanofretting is three orders magnitude smaller than that in fretting; (iii) the friction coefficient in nanofretting is much lower than that in fretting in slip regime; (iv) no obvious damage was observed after 50 cycles of nanofretting under a normal load of 10 mN.<br /

Determination of transformation stresses of shape memory alloy thin films : a method based on spherical indentation

The forward and reverse transformation processes of superelastic shape memory alloys (SMAs) under spherical indentation are analyzed. We found that there exist two characteristic points, the bifurcating point and the returning point, in an indentation curve. The corresponding bifurcation force and return force, respectively, rely on the forward transformation stress and the reverse transformation stress. A method to determine the transformation stresses of SMA from the measure of the bifurcation and return forces is proposed. Additionally, we suggest a slope approach to determine the values of the two forces with high accuracy. (c) 2006 American Institute of Physics

Tri11, tri3, and tri4 genes are required for trichodermin biosynthesis of Trichoderma brevicompactum

Abstract Trichoderma brevicompactum and T. arundinaceum both can synthesize trichodermin with strong antifungal activity and high biotechnological value. The two Trichoderma species have a tri cluster, which includes seven genes (tri14, tri12, tri11, tri10, tri3, tri4, and tri6) that encode transport and regulatory enzymes required for the biosynthesis of trichodermin. Here, we isolated T. brevicompactum 0248 transformants with disrupted tri11, tri4, or tri3 gene. We also described the effect of tri11, tri3, or tri4 deletion on the expression of other genes in the tri cluster. Targeted Δtri3 knockout mutant exhibited a sharp decline in the production of trichodermin, and trichodermol, which is a substrate for trichodermin production, accumulated. Thus, the results demonstrated that tri3 was responsible for the biosynthesis of trichodermin, and the tri3 gene-encoded enzyme catalyzed the acetylation reaction of the hydroxy group at C-4 of the trichodermin skeleton. In addition, tri4 and tri11 deletion mutants were generated to evaluate the roles of tri4 and tri11 in trichodermin biosynthesis, respectively. Deletion mutant strain Δtri4 or Δtri11 did not produce trichodermin in T. brevicompactum, indicating that tri4 and tri11 are essential for trichodermin biosynthesis. This is the first to report the function of tri3, tri4 and tri11 in T. brevicompactum, although the role of tri4 and tri11 has already been described for T. arundinaceum by Cardoza et al. (Appl Environ Microbiol 77:4867–4877, 2011)

Recent intensified erosion and massive sediment deposition in Tibetan Plateau rivers

Abstract Recent climate change has caused an increase in warming-driven erosion and sediment transport processes on the Tibetan Plateau (TP). Yet a lack of measurements hinders our understanding of basin-scale sediment dynamics and associated spatiotemporal changes. Here, using satellite-based estimates of suspended sediment, we reconstruct the quantitative history and patterns of erosion and sediment transport in major headwater basins from 1986 to 2021. Out of 13 warming-affected headwater regions, 63% of the rivers have experienced significant increases in sediment flux. Despite such intensified erosion, we find that 30% of the total suspended sediment flux has been temporarily deposited within rivers. Our findings reveal a pronounced spatiotemporal heterogeneity within and across basins. The recurrent fluctuations in erosion-deposition patterns within river channels not only result in the underestimation of erosion magnitude but also drive continuous transformations in valley morphology, thereby endangering local ecosystems, landscape stability, and infrastructure project safety

Graphene Failure under MPa: Nanowear of Step Edges Initiated by Interfacial Mechanochemical Reactions

The low wear resistance of macroscale graphene coatings does not match the ultrahigh mechanical strength and chemical inertness of the graphene layer itself; however, the wear mechanism responsible for this issue at low mechanical stress is still unclear. Here, we demonstrate that the susceptibility of the graphene monolayer to wear at its atomic step edges is governed by the mechanochemistry of frictional interfaces. The mechanochemical reactions activated by chemically active SiO2 microspheres result in atomic attrition rather than mechanical damage such as surface fracture and folding by chemically inert diamond tools. Correspondingly, the threshold contact stress for graphene edge wear decreases more than 30 times to the MPa level, and mechanochemical wear can be described well with the mechanically assisted Arrhenius-type kinetic model, i.e., exponential dependence of the removal rate on the contact stress. These findings provide a strategy for improving the antiwear of graphene-based materials by reducing the mechanochemical interactions at tribological interfaces

Definition of Atomic-Scale Contact: What Dominates the Atomic-Scale Friction Behaviors?

The definition of atomic-scale contact is a very ambiguous issue owing to the discrete atomic arrangement, which hinders the development of contact theory and nano-tribological techniques. In this work, we studied the atomic-scale contact area and their correlations with friction force based on three distinct contact definitions (interatomic distance, force, and interfacial chemical bonds) by performing large-scale atomistic simulations on a typical ball-on-disk contact model. In the simulations, the measured contact areas defined by interatomic distance, force, and interfacial chemical bonds (referred as to Adist, Aforce, and Abond, respectively) are not equivalent at all, while we interestingly clarify that only Adist is consistent with the one calculated by continuum Hertz contact mechanics, and moreover, only Abond is proportional to the friction force indicating that Abond is the dominant one for determining materials’ frictional behaviors. The above fundamental insights into the atomic-scale contact problems are useful to deeply understand the origins of tribological phenomena and contribute to the further prediction of atomic-scale friction

MOESM2 of Tri11, tri3, and tri4 genes are required for trichodermin biosynthesis of Trichoderma brevicompactum

Additional file 2: Table S2. Primers used for qRT-PCR