Investigation of hardness behavior after carburizing and hardening of 15CrNi6 steel

DIN 15CrNi6 is the most representative grade of the case-hardened steels. The present work analyses the influence of carburizing time on hardness of the specific steel. Specimens with similar chemical composition were heated at 900°C in liquid carbonaceous media for one, two, three and four hours, correspondingly. Then samples were oil quenched and tempered at 180°C for two hours. Microhardness was measured across the carburized zone and case profiles were acquired. The effective case depth was determined as function of carburizing holding time. Core macro hardness was carried out and the impact of holding time on the substrate hardness was discussed. The optimum case depth was defined and the carburizing parameters determined. The hardness control is critical in case hardening practice and results provide practical information to heat treaters, useful both to control the treatment parameters and to minimize the risk of failure.

New ichnofabrics of the Cenomanian–Danian Chalk Group

ABSTRACT The Cenomanian–Danian Chalk Group of NW Europe is characterized by distinct trace-fossil assemblages dominated by Thalassinoides isp., Planolites isp., Zoophycos isp., and Chondrites isp., whereas ichnogenera such as Taenidium and Phycosiphon are rare. The trace fossils form a complex tiering arrangement, which reflects burrowing activities of diverse benthic associations that operate at different levels in the sediment column, dynamic sedimentation rates, and changes in substrate hardness during progressive burial, forming intricate ichnofabrics. In the Danish Basin, studies of chalk ichnofabrics have focused mainly on the Maastrichtian. Studies of the shallower, grain-rich Danian chalk have revealed similar trace-fossil assemblages, whereas the ichnology of the fine-grained, deeper-water Danian deposits is poorly known. Based on detailed facies and ichnofabric analysis of a mid-Danian silica-rich, pelagic chalk located in the central, deeper shelf area of the Danish Basin, four facies types, eight ichnotaxa, and two ichnofabrics are recognized. Most conspicuous and abundant are randomly distributed, variously sized meniscate burrows attributed to Bichordites isp. and Taenidium isp., whereas other common chalk trace fossils are rare or absent. This trace-fossil assemblage outlines two new ichnofabrics in the NW European chalk, which are dominated principally by upper-tier traces. The producer of the abundant Bichordites isp. and Taenidium isp. burrows is identified as a sea urchin on the basis of an exceptionally preserved Bichordites isp. trace aligned with an irregular echinoid body fossil. The identified ichnofabrics controlled early silicification and produced a more complex distribution of silica concretions compared with chalk successions elsewhere. This results in volumetrically thick silica concretion-rich units rather than distinctive silica bands as seen in other Upper Cretaceous and Danian chalk units.

Experimental Study for the Stripping of PTFE Coatings on Al-Mg Substrates Using Dry Abrasive Materials

Polytetrafluoroethylene (PTFE) coatings are used in many applications and processing industries. With their use, they wear out and lose properties and must be replaced by new ones if the cost of the element so advises. There are different stripping techniques, but almost all of them are very difficult and require strict environmental controls. It is a challenge to approach the process through efficient and more sustainable techniques. In the present work, we have studied the stripping of PTFE coatings by projection with abrasives (1 step) as an alternative to carbonization + sandblasting procedures (2 steps). For this purpose, different types of abrasives have been selected: brown corundum, white corundum, glass microspheres, plastic particles, and a walnut shell. The tests were performed at pressures from 0.4 to 0.6 MPa on PTFE-coated aluminium substrates of EN AW-5182 H111 alloy. Stripping rates, surface roughness, and substrate hardness have been studied. Scanning electron microscopy (SEM) images of sandblasted specimens have also been obtained. All abrasives improved mechanical and surface properties in one-step vs. two-step processes. The abrasives of plastic and glass microspheres are the most appropriate for the one-step process, which increases the hardness and roughness level Ra in the substrate. Corundum abrasives enable the highest stripping rates.

Effect of Process Parameters on Microstructure and Mechanical Properties of Direct Laser Deposited Cold-Resistant Steel 09CrNi2MoCu for Arctic Application

Effect of process parameters of microstructure formation and mechanical properties of direct laser deposited parts of cold-resistant steel 09CrNi2MoCu is studied. Due to local properties of buildup depends on thermal cycle during fabrication simulation of temperature field was carried out. The following cases were analysed: deposition of the first layer on massive substrate and deposition of a layer on the buildup far from the substrate. It was established that one time high temperature reheating of deposited layer has no effect on hardness while additional reheating up to lower temperature leads to considerable decrease in hardness by 87-100 HV. Far from substrate hardness and microstructure bands of 0.7-0.8 mm thickness have a hardness variation in the range of 250-300 HV. The area close to the substrate has a microstructure of upper bainite with higher hardness due to higher cooling rates during deposition. In the process of deposited, at a higher power, a quick process of heating and cooling occurs, and vice versa, which forms various products of bainite transformation. From the obtained modes were presented the results of tests for impact strength at low temperatures.

Sweet neurons inhibit texture discrimination by signaling TMC-expressing mechanosensitive neurons in Drosophila

Integration of stimuli of different modalities is an important but incompletely understood process during decision making. Here, we show that Drosophila are capable of integrating mechanosensory and chemosensory information of choice options when deciding where to deposit their eggs. Specifically, females switch from preferring the softer option for egg-laying when both options are sugar free to being indifferent between them when both contain sucrose. Such sucrose-induced indifference between options of different hardness requires functional sweet neurons, and, curiously, the Transmembrane Channel-like (TMC)-expressing mechanosensitive neurons that have been previously shown to promote discrimination of substrate hardness during feeding. Further, axons of sweet neurons directly contact axons of TMC-expressing neurons in the brain and stimulation of sweet neurons increases Ca2+ influx into axons of TMC-expressing neurons. These results uncover one mechanism by which Drosophila integrate taste and tactile information when deciding where to deposit their eggs and reveal that TMC-expressing neurons play opposing roles in hardness discrimination in two different decisions.

Effect of substrate hardness and surface roughness on the film formation of aerosol-deposited ceramic films

The aerosol deposition (AD) method is a novel ceramic coating technique that allows manufacturing of dense ceramic films at room temperature directly from ceramic powders without any high temperature sintering steps and without expensive (ultra) high vacuum processes. The deposition mechanism can be separated into two stages: the creation of an anchor layering and the subsequent film formation. Step one involves an initial plastic deformation of the substrate surface by the first impacting particles. Especially in the first stage, substrate properties affect the deposition and determine the dominant bonding mechanism. Ductile substrates can be expected to give strong film anchoring, whereas high hardness substrates might require higher particle velocities to form adhering layers. In this study, the influence of the substrate hardness in combination with the surface roughness on the deposition was investigated. Four ceramic substrates (two types of Al2O3, sapphire, and LTCC) with different hardness and surface roughness were coated with Al2O3 in order to study the formation of an anchoring layer and their effect on the deposition rate. As a result, no anchoring layer was found on the hard ceramic substrates.

Kinetic Study of the Growth of Hard Layers on a Low Carbon Steel

ABSTRACTIn the present work the kinetic growth is analyzed for a hard coating applied on a low carbon steel AISI 8620. A thermochemical treatment of bored with dehydrated paste at temperatures of 900, 950 and 1000 °C with a residence time of 2, 4, 6 and 8 h. The morphology and types of borides formed on the surface of the steel were evaluated by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The layer formed has a size of 20 to 113 μm which will be dependent on the process temperature, the treatment time and the alloy elements of the substrate. Hardness of 1493-1852 HV are presented for treatment times and temperatures established in this study. The kinetics of growth were determined and analyzed using a mathematical model of diffusion, evaluating the penetration of the biphasic layer that is determined as a function of the time and temperature of the thermochemical treatment (TCT). The results show the increase in the growth constants (k) with respect to the bored temperatures. The activity energy (Q) of the material AISI 8620 was also obtained.