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Failure mode analysis of coated tools
Classified abstracts 6 5 4 1 - 6 5 4 8 or spall through the growth of cracks, presumably initiated at the metal coating interface or at the substrate. The present study was undertaken to determine whether such cracks are at the s u b s t r a t e ~ o a t i n g interface or within the coating or the substrate themselves. An AISI 1045 steel overlayed with a nickel~zhrome alloy was used and the samples were subjected to a positive stress and fatigued using sinusoidal oscillations. In order to obtain a continuous record of crack initiation and propagation, acoustic emission equipment was used. The variation of the events and count rates and energy liberated per event made it possible to determine crack initiation and to follow crack growth. Scanning electron microscopy was used to examine sections of the specimens at different stages o f the real-time graphs of acoustic emission. It was found that the cracks initiated in the coating near the interface and not at the substrate or interface as suggested elsewhere. The conditions promoting crack initiation were also determined. J G Mora-Marquez and J Lira-Olivares, Thin Solid Films, 153, 1987, 243552.
22 6541. Failure mode analysis of coated tools Coated metal-cutting tools that did not perform to expectations were analysed for the reasons of their premature failure. These tools investigated stem from two sources: regular users of coated tools who noticed a premature failure of a single tool or a production lot or first users who were disappointed not to obtain the expected performance gains. Optical microscopy, adhesion tests, metallography, scanning electron microscopy, energy-dispersive X-ray analysis. Auger spectroscopy, secondary ion mass spectrometry and drilling with reference tools were used as methods of investigation. Reasons for premature failure are related to the following: substrate material selection, metallurgy and heat treatment; tool manufacturing with respect to edge finish, surface finish and presence of Beilby layers; the various steps of the coating process (pretreatment, heating, etching, coating and conditioning); end user. Coating wear (intrinsic) is not treated in this analysis. The method is demonstrated with 11 case studies. E Bergmann et al, Thin Solid Films, 153, 1987, 219 231.
22 6542. The influence of the TiN deposition temperature on the critical load and hardness of hardened steels Hard thin TiN films are extensively used as wear-resistant coatings on high speed steel tools. So far these films have not been used on other types o f steel. In this work, TiN was reactively sputter deposited onto high speed steel, tool steel, case-hardening steel and silicon iron. The critical load and its dependence on deposition temperature were determined. The critical load increases when the temperature increases above 250°C as the different steels start to decarburize. Above 500°C the critical load decreases to its lowest value for all the steels tested except for high speed steel. M Y AI-Jaroudi et al, Thin Solid Films, 154, 1987, 4 2 5 4 2 9 .
22 6543. The relationship between hardness and scratch adhesion Microhardness and scratch adhesion testing are the most commonly used techniques for assessing the mechanical properties of thin surface coatings such as physical vapour-deposited TiN. Both of these test methods utilize single-point contacts, a diamond pyramid for microhardness testing and usually a Rockwell C 120 ° diamond cone for scratch testing, and both induce plastic deformation in the substrate and coating. Clearly, static microhardness and scratch adhesion testing will have c o m m o n features, since, in both, the plastic deformation processes are likely to be similar. An analysis based on elasti~plastic indentation theory has been developed that allows both the prediction of the hardness of a given coating-substrate system and the estimation of shear strains developed at the coating-substrate interface which, for weakly adhered films, leads to delamination of the coating around an indentation. The ideas embodied in the volume law-of-mixtures hardness model have also been applied to the scratch test, allowing estimates to be made of the interfacial shear strains present during testing since these contribute to the measured "critical load" Lc for coating failure. The rote of substrate plastic deformation and other factors affecting L~ (such as friction, internal stress and coating thickness) will be discussed. P J Burnett and D S Rickerby, Thin Solid Films, 154, 1987, 4 0 3 4 1 6 . 500
22 6544. Evaluation of adhesion strength of thin hard coatings Extensive research has been carried out in order to study the feasibility of various methods for evaluating the adhesion strength of thin hard coatings, produced by a wide variety of coating methods, to steels. Indentation, scratch, hammering, rolling with slip, and coining and metal stamping tests were employed and some of them were concluded to be of no use for such thin hard coatings which have large adhesion strength. Carbide and nitride coatings produced by high temperature processes such as chemical vapour deposition (CVD) and salt bath immersion showed less failure by all testing methods than those produced by low temperature processes such as physical vapour deposition, low temperature C V D and c h r o m i u m plating. However, TiN coatings formed by plasma-assisted C V D at low temperature showed less failure than those formed by sputtering and ion plating. T Arai et al, Thin Solid Films, 154, 1987, 3 8 7 4 0 1 . 22 6545. Adhesion measurements of chemically vapor deposited and physically vapor deposited hard coatings on W C - C o substrates Comparative measurements of adhesion of single-layer and multilayer hard coatings on cemented carbide substrates are made using scratch and indentation test methods. It is shown that the critical loan L c in scratch adhesion is influenced by the hardness of the substrate and extraneously by the surface condition of the indenter and its coefficient of friction relative to the coating material. The average stress calculated from the width of the scratch channel is found to be a more meaningful adhesion parameter than Lc. In the indentation technique, the approximate load for lateral crack initiation and the slope obtained from the indentation load lateral crack length function are two useful adhesion parameters. The latter is demonstrated to be more discriminating in several test cases. It is also found that increased residual stress in physically vapor deposited TiN coating reduces both measured scratch and indentation adhesion parameters. Prem C Jindal et al, Thin Solid Films, 154, 1987, 361 375. 22 6546. The effect of nitrogen content on the critical normal force in scratch testing of T i N films The scratch test method was used to study the effect of nitrogen content on the critical normal force of Ti N films on stainless steel and high speed steel substrates. The critical normal force decreased strongly with decreasing nitrogen concentration, which m a y be explained by the corresponding decrease in the elastic modulus which has recently been reported. Three distinctively different regions were observed with increasing nitrogen content. The first was the titanium region, which showed gross plastic deformation typical of soft films. The second was a transition region while the third finally showed the typical cracking pattern of hard films as evidenced by the appearance of cracks perpendicular to the scratching direction. The coefficient of friction at the m o m e n t of attainment of the critical normal force was found to agree well with the theory of abrasive wear but no simple correlation was found between the coefficient of friction and the critical normal force. J Valli et al, Thin Solid Films, 154, 1987, 351 360. 22 6547. Thin film characterization using a mechanical properties microprobe A new ultra-low load microindentation system has been acquired in the Metals and Ceramics Division of Oak Ridge National Laboratory. The system's spatial resolution and its data acquisition capabilities allow the determination o f several mechanical properties from volumes of material with submicron d i m e n s i o n - - h e n c e the term mechanical properties and microprobe (MPM). Research with the M P M at Oak Ridge has led to improved techniques for determining the plastic and elastic properties of materials using microindentation experiments. The techniques have been applied to thin films created by ion implanting metals and ceramics, radiation damaged materials and thin hard coatings of TiN. Changes in the strength (hardness) and modulus have been measured in films as thin at 200 nm. W C Oliver ct al, Thin Solid Films, 153, 1987, 185 196. 22 6548. The interrelationship between internal stress, processing parameters and microstrueture of physically vapour deposited and thermally sprayed coatings Internal stress is an important parameter in coating technology since it
22 6541. Failure mode analysis of coated tools Coated metal-cutting tools that did not perform to expectations were analysed for the reasons of their premature failure. These tools investigated stem from two sources: regular users of coated tools who noticed a premature failure of a single tool or a production lot or first users who were disappointed not to obtain the expected performance gains. Optical microscopy, adhesion tests, metallography, scanning electron microscopy, energy-dispersive X-ray analysis. Auger spectroscopy, secondary ion mass spectrometry and drilling with reference tools were used as methods of investigation. Reasons for premature failure are related to the following: substrate material selection, metallurgy and heat treatment; tool manufacturing with respect to edge finish, surface finish and presence of Beilby layers; the various steps of the coating process (pretreatment, heating, etching, coating and conditioning); end user. Coating wear (intrinsic) is not treated in this analysis. The method is demonstrated with 11 case studies. E Bergmann et al, Thin Solid Films, 153, 1987, 219 231.
22 6542. The influence of the TiN deposition temperature on the critical load and hardness of hardened steels Hard thin TiN films are extensively used as wear-resistant coatings on high speed steel tools. So far these films have not been used on other types o f steel. In this work, TiN was reactively sputter deposited onto high speed steel, tool steel, case-hardening steel and silicon iron. The critical load and its dependence on deposition temperature were determined. The critical load increases when the temperature increases above 250°C as the different steels start to decarburize. Above 500°C the critical load decreases to its lowest value for all the steels tested except for high speed steel. M Y AI-Jaroudi et al, Thin Solid Films, 154, 1987, 4 2 5 4 2 9 .
22 6543. The relationship between hardness and scratch adhesion Microhardness and scratch adhesion testing are the most commonly used techniques for assessing the mechanical properties of thin surface coatings such as physical vapour-deposited TiN. Both of these test methods utilize single-point contacts, a diamond pyramid for microhardness testing and usually a Rockwell C 120 ° diamond cone for scratch testing, and both induce plastic deformation in the substrate and coating. Clearly, static microhardness and scratch adhesion testing will have c o m m o n features, since, in both, the plastic deformation processes are likely to be similar. An analysis based on elasti~plastic indentation theory has been developed that allows both the prediction of the hardness of a given coating-substrate system and the estimation of shear strains developed at the coating-substrate interface which, for weakly adhered films, leads to delamination of the coating around an indentation. The ideas embodied in the volume law-of-mixtures hardness model have also been applied to the scratch test, allowing estimates to be made of the interfacial shear strains present during testing since these contribute to the measured "critical load" Lc for coating failure. The rote of substrate plastic deformation and other factors affecting L~ (such as friction, internal stress and coating thickness) will be discussed. P J Burnett and D S Rickerby, Thin Solid Films, 154, 1987, 4 0 3 4 1 6 . 500
22 6544. Evaluation of adhesion strength of thin hard coatings Extensive research has been carried out in order to study the feasibility of various methods for evaluating the adhesion strength of thin hard coatings, produced by a wide variety of coating methods, to steels. Indentation, scratch, hammering, rolling with slip, and coining and metal stamping tests were employed and some of them were concluded to be of no use for such thin hard coatings which have large adhesion strength. Carbide and nitride coatings produced by high temperature processes such as chemical vapour deposition (CVD) and salt bath immersion showed less failure by all testing methods than those produced by low temperature processes such as physical vapour deposition, low temperature C V D and c h r o m i u m plating. However, TiN coatings formed by plasma-assisted C V D at low temperature showed less failure than those formed by sputtering and ion plating. T Arai et al, Thin Solid Films, 154, 1987, 3 8 7 4 0 1 . 22 6545. Adhesion measurements of chemically vapor deposited and physically vapor deposited hard coatings on W C - C o substrates Comparative measurements of adhesion of single-layer and multilayer hard coatings on cemented carbide substrates are made using scratch and indentation test methods. It is shown that the critical loan L c in scratch adhesion is influenced by the hardness of the substrate and extraneously by the surface condition of the indenter and its coefficient of friction relative to the coating material. The average stress calculated from the width of the scratch channel is found to be a more meaningful adhesion parameter than Lc. In the indentation technique, the approximate load for lateral crack initiation and the slope obtained from the indentation load lateral crack length function are two useful adhesion parameters. The latter is demonstrated to be more discriminating in several test cases. It is also found that increased residual stress in physically vapor deposited TiN coating reduces both measured scratch and indentation adhesion parameters. Prem C Jindal et al, Thin Solid Films, 154, 1987, 361 375. 22 6546. The effect of nitrogen content on the critical normal force in scratch testing of T i N films The scratch test method was used to study the effect of nitrogen content on the critical normal force of Ti N films on stainless steel and high speed steel substrates. The critical normal force decreased strongly with decreasing nitrogen concentration, which m a y be explained by the corresponding decrease in the elastic modulus which has recently been reported. Three distinctively different regions were observed with increasing nitrogen content. The first was the titanium region, which showed gross plastic deformation typical of soft films. The second was a transition region while the third finally showed the typical cracking pattern of hard films as evidenced by the appearance of cracks perpendicular to the scratching direction. The coefficient of friction at the m o m e n t of attainment of the critical normal force was found to agree well with the theory of abrasive wear but no simple correlation was found between the coefficient of friction and the critical normal force. J Valli et al, Thin Solid Films, 154, 1987, 351 360. 22 6547. Thin film characterization using a mechanical properties microprobe A new ultra-low load microindentation system has been acquired in the Metals and Ceramics Division of Oak Ridge National Laboratory. The system's spatial resolution and its data acquisition capabilities allow the determination o f several mechanical properties from volumes of material with submicron d i m e n s i o n - - h e n c e the term mechanical properties and microprobe (MPM). Research with the M P M at Oak Ridge has led to improved techniques for determining the plastic and elastic properties of materials using microindentation experiments. The techniques have been applied to thin films created by ion implanting metals and ceramics, radiation damaged materials and thin hard coatings of TiN. Changes in the strength (hardness) and modulus have been measured in films as thin at 200 nm. W C Oliver ct al, Thin Solid Films, 153, 1987, 185 196. 22 6548. The interrelationship between internal stress, processing parameters and microstrueture of physically vapour deposited and thermally sprayed coatings Internal stress is an important parameter in coating technology since it