High Hot Hardness Research Articles

Thermal stability of silicon‐doped Al2O3 PVD coatings

AbstractCrystalline alumina PVD‐coatings offer high potential for different applications in which high chemical inertness, high hot hardness and high oxidation resistance is important. Especially the metastable γ‐phase is topic of many researches because, in comparison to the stable α‐phase, it can be deposited by means of MSIP (Magnetron Sputter Ion Plating) at relatively low process temperatures below 650°C and it is more fine‐grained than α‐Al2O3. At high temperatures γ‐Al2O3 transforms into α‐Al2O3, which limits the application temperature. But until now it is not clearly understood, up to which temperatures γ‐Al2O3 coatings are stable and which mechanisms influence the stability. In this paper the influence of doping with silicon is investigated. DSC (differential scanning calorimetry) as well as XRD (X‐Ray diffractometry) measurements show that adding 4 at% silicon leads to a high amount of amorphous phase in the as deposited coating and a decrease of hardness from 18 GPa to 10 GPa. Nevertheless, formation of α‐phase is retarded to temperatures above 1200°C while α‐phase is formed at 1100°C for the undoped coating. A transformation via the θ‐phase was detected for the Si‐doped coating, which is not seen for undoped coating.

Enhanced ultrasonically assisted turning of a β-titanium alloy

Although titanium alloys have outstanding mechanical properties such as high hot hardness, a good strength-to-weight ratio and high corrosion resistance; their low thermal conductivity, high chemical affinity to tool materials severely impair their machinability. Ultrasonically assisted machining (UAM) is an advanced machining technique, which has been shown to improve machinability of a β-titanium alloy, namely, Ti-15-3-3-3, when compared to conventional turning processes.

The Applied Mechanics Control System for Removal Manipulator Based on Mechanical Materials and its Application

After analyzing the movement requirements of the manipulators, we selected the movement form and control system of the manipulators, and do the PLC programming according to the movement flowchart of the manipulators. The manipulators can continue working under the poor working conditions, so that improve the working conditions for the workers, reduce labor intensity, and Raise the level of automation. The material of the manipulator clamping device was required that has good durability and abrasion resistance, hardenability carburizing steels 20CrNi3 is selected. After carburizing, quenching and low-temperature tempering, the alloy element and the carbon come together to form a sufficient number of carbide and martensite when heat treatment, guaranteeing high hardness, abrasion resistance and hot hardness, high alloy element content also improves the hardenability and temper resistance to ensure enough strength and toughness.

Machinability Study of Cemented Carbide Using Focused Ion Beam (FIB) Milling

Focused ion beam (FIB) milling is one of the fastest and accurate processes for the micro- and nanofabrication of devices. There is a need of making micro- and nanoscale components from cemented carbide material due to its favorable properties of high hot hardness and wear resistance. These are the required properties of a microtool during micromachining. Efforts have been put forward to investigate the machinability aspects of cemented carbide by the FIB milling process. Beam current was observed as the significant process parameters of FIB milling process to affect the material removal rate (MRR) and surface roughness on the machined surface of cemented carbide. In addition, extraction voltage, angle of beam incidence, and percentage overlap between beam diameters of adjacent pixels were taken into account to analyze the machinability aspects of cemented carbide by FIB milling. Dwell time was observed as a less significant parameter to affect MRR and surface roughness of cemented carbide.

Crystalline <I>γ</I>-Al<SUB>2</SUB>O<SUB>3</SUB> Physical Vapour Deposition-Coating for Steel Thixoforging Tools

The process of thixoforming, which has been part of many researches during the last decades, combines the advantages of forging and casting for the shaping of metallic components. But due to the high temperatures of semi-solid steel alloys high demands on the tools are requested. To resists the thermal and mechanical loads (wear, friction, thermal and thermomechanical fatigue) protecting thin films are necessary. In this regard crystalline gamma-Al2O3 deposited via Physical Vapour Deposition (PVD) is a promising candidate: It exhibits high thermal stability, high oxidation resistance and high hot hardness. In the present work the application of a (Ti, Al)N/gamma-Al2O3 coating deposited by means of Magnetron Sputter Ion Plating in an industrial coating unit is presented. The coating was analysed by means of Rockwell test, nanoindentation, and Scanning Electron Microscopy (SEM). The coated tool was tested in thixoforging experiments with steel grade X210CrW12 (AlSI D6). The surface of the coated dies was examined with Scanning Electron Microscope (SEM) after 22, 42, 90 and 170 forging cycles.

Study of surface quality in high speed turning of Inconel 718 with uncoated and coated CBN tools

Inconel 718 is known to be among the most difficult-to-machine materials due to its special properties which cause the short tool life and severe surface damages. The properties, which are responsible for poor machinability, include rapid work hardening during machining; tendency to weld with the tool material at high temperature generated during machining; the tendency to form a built-up edge during machining; and the presence of hard carbides, such as titanium carbide and niobium carbide, in their microstructure. Conventional method of machining Inconel 718 with cemented carbide tool restricts the cutting speed to a maximum 30 m/min due to the lower hot hardness of carbide tool, high temperature strength and low thermal conductivity of Inconel 718. The introduction of new coated carbide tools has increased cutting speed to 100 m/min; nevertheless, the time required to machine this alloy is still considerably high. High speed machining using advanced tool material, such as CBN, is one possible alternative for improving the productivity of this material due to its higher hot hardness in comparison with carbide tool. This paper specifically deals with surface quality generated under high speed finishing turning conditions on age-hardened Inconel 718 with focus on surface roughness, metallographic analysis of surface layer and surface damages produced by machining. Both coated and uncoated CBN tools were used in the tests, and a comparison between surfaces generated by both tools was also discussed.

Drilling of composite and titanium stacks with alternating machining parameters by PCD drill

Drilling of multilayer materials with conventional machining parameters are selected in such a way that it suits the requirements of both composite and metal, which is already unsuitable for machining high holes quality due to differential mechanical and thermal properties of stacks. The present study attempts a newer research on drilling of carbon fibre reinforced plastics (CFRP) and titanium stacks with alternating machining parameters by PCD drill in order to minimise the delamination of CFRP and burrs in titanium alloy. Results show that drilled holes quality can be improved by optimising the drilling parameters for each material. It was found that PCD drill outperformed better in drilling CFRP-titanium stacks for its high hot hardness and wear resistance. From the 25th to 50th hole, the thrust force of CFRP laminates is stable of 60±5 N owing to normal wear stage. This region is ideal for the drilling performance of PCD drill.

Thermal stability of γ-Al 2O 3 coatings for challenging cutting operations

Crystalline PVD Al 2O 3 coatings offer great potential for their use in cutting operations. They promise high hot hardness and high oxidation resistance at elevated temperatures. Alumina exists in different crystallographic phases. α-Al 2O 3 appears to be the only thermodynamically stable phase at all common temperatures and pressures. Today there are many efforts to generate α-Al 2O 3 by means of physical vapour deposition. In this regard one problem is the high deposition temperature, which does not allow the deposition on temperature-sensitive materials. Another promising candidate is γ-Al 2O 3 which is more fine-grained than α-Al 2O 3 and can be deposited at lower temperatures. At high temperatures γ-Al 2O 3 might be transformed into α-Al 2O 3, which could limit the application temperature. But until now it is not clearly proved, up to which temperatures γ-Al 2O 3 thin films are stable and which mechanisms influence the stability. In the present work different (Ti,Al)N/γ-Al 2O 3 coatings are deposited on cemented carbides by means of Magnetron Sputter Ion Plating (MSIP). The (Ti,Al)N bond coat was employed to improve adhesion of γ-Al 2O 3 on the substrate. It could be shown that the γ-phase is stable in vacuum up to 1200 °C. In the atmosphere the formation of α-Al 2O 3 begins at 900 °C and it is influenced by the choice of transition zone between the (Ti,Al)N interlayer and γ-Al 2O 3. The results show that the thermal stability of the γ-phase and therefore the application temperature of the coating can be enhanced by the choice of interlayer.

Microstructure and Mechanical Properties of New AlCoxCrFeMo0.5Ni High‐Entropy Alloys

AbstractEffects of Co content on microstructures and hot hardness of a new high‐entropy alloy system, AlCoxCrFeMo0.5Ni (x = 0.5 to 2.0) were investigated. As cobalt content increases, the microstructure changes from dendrite to polygrain type and the constituent phases change from BCC + σ at x = 0.5 to BCC + FCC + σ at x = 2.0. The alloy hardness varies from Hv 788 at x = 0.5 to Hv 596 at x = 2.0. This can be explained with the relative amount of hard σ phase, medium hard BCC phase and soft FCC phase. All the AlCoxCrFeMo0.5Ni alloys possess higher hardness level than that of Ni‐based superalloys In 718/In 718 H from room temperature to 1273 K. They obey the Westbrook equation presenting the normal heating behavior. Both alloys of x = 0.5 and 1.0 exhibit a transition temperature higher than that of Co‐based alloy T‐800 by about 200 K. They also have a high hot hardness of Hv 347 at 1273 K, which is higher than those of In 718 and In718 H by Hv 220. The strengthening mechanism for their superiority is proposed. The AlCoxCrFeMo0.5Ni alloy system has great potential in high‐temperature applications.

Crystalline γ‐Alumina Deposited in an Industrial Coating Unit for Demanding Turning Operations

AbstractCrystalline PVD γ‐Al2O3‐ coatings offer great potential for their use in high‐speed cutting operations. They promise high hot hardness and high oxidation resistance at elevated temperatures. This is important for coatings that are used for machining of materials with low thermal conductivity such as stainless steel or Inconel 718 because heat generated during cutting can barely be dissipated by the chip. Because of the prevailing bonding forces of alumina, adhesion‐related sticking can be reduced even for dry cutting. Furthermore, the high formation enthalpy of alumina prevents chemical reactions with frictional partners. The present work gives an overview of the deposition of γ‐Al2O3 thin films on WC/Co‐cutting inserts by using pulsed MSIP (magnetron sputter ion plating) PVD technology. To improve adhesion, a (Ti,Al)N bond coat was employed. The samples were analyzed using common thin film test equipment. Cutting tests and pin‐on‐disk examinations were carried out to test the coating's performance. For turning operations, the difficult‐to‐machine austenitic steel 1.4301 (X5CrNi18‐10) was used. In comparison to a state‐of‐the‐art (Ti,Al)N coating, (Ti,Al)N/γ‐Al2O3 showed a longer tool life.

Design and performance of AlTiN and TiAlCrN PVD coatings for machining of hard to cut materials

Abstract Machining of hard to cut materials such as hardened steels and high temperature strong aerospace materials is a challenge of modern manufacturing. Two categories of the aluminum-rich TiAlN-based Physical Vapor Deposited (PVD) coatings, namely AlTiN and TiAlCrN, are commonly used for this area of application. A comparative investigation of the structural characteristics, various micro-mechanical properties, oxidation resistance and service properties of the both coatings has been performed. Crystal structure has been studied using High Resolution Transmission Electron Microscopy (HR TEM). Electronic structure has been investigated using X-ray Photoelectron Spectroscopy (XPS). Micro-mechanical properties (microhardness, plasticity index, impact fatigue fracture resistance) have been evaluated using a Micro Materials Nano-Test System. Short-term oxidation resistance has been studied at 900 °C in air. The tool life of the coating was studied during ball nose end milling of hardened H 13 tool steel as well as end milling of aerospace alloys such as Ni-based superalloy (Waspalloy) and Ti alloy (TiAl6V4). It was shown that the set of characteristics that control wear performance strongly depend on specific applications. For machining of hardened tool steels, when heavy loads/high temperatures control wear behavior, the coating has to possess a well-known combination of high hot hardness and improved oxidation resistance at elevated temperatures. To achieve these properties, crystal structure for TiAlN-based coatings should be mainly B1, and elemental composition of the coating should ensure formation of strong inter-atomic bonds such as Al–Cr metal-covalent bonds in the TiAlCrN coating. Nano-crystalline structure with grain size of around 10–30 nm enhances necessary properties of the coating. In contrast, for machining of aerospace alloys, when elevated load/temperature combined with intensive adhesive interaction with workpiece material results in unstable attrition wear with deep surface damage, the coating should possess a different set of characteristics. Crystal structure for TiAlN-based coatings is basically B1; but due to a high amount of aluminum, the AlTiN coating contains AlN domains. The coating has a very fine-grained nano-crystalline structure (grains sized around 5 nm). Electron structure of energy levels indicates formation of metallic bonds. This results in plasticity increase at the cost of hot hardness reduction. The surface is able to dissipate energy by means of plastic deformation (instead of crack formation) and in this way, surface damage is reduced.

Thermal Investigation of Al2O3 Thin Films for Application in Cutting Operations

Crystalline PVD γ-Al2O3 coatings offer great potential for use in high-speed cutting operations. They offer specific high temperature features, like high hot hardness and high oxidation resistance. However, the reasons for the high thermal stability of this system are not clearly understood. In this paper, the phase and oxidation stability of thin γ-Al2O3 films (as illustrated in the micrograph) are investigated.

The performance of polycrystalline cubic boron nitride tools in continuous, semi-interrupted, and interrupted hard machining

Polycrystalline cubic boron nitride (PCBN) cutting tools have enabled large-scale industrial hard machining owing to their high hot hardness and wear resistance. Experience clearly shows that tool requirements vary depending on the presence and severity of interrupts in the workpiece. The interrelationships between workpiece interruption parameters and tool wear and performance are assessed using a programme of continuous, semi-interrupted, and interrupted hard machining tests. A hypothesis for observed variations in wear behaviour between different PCBN grades and test conditions is developed on the basis of detailed tool wear scar analyses.

Coating optimisation for high speed machining with advanced nanomechanical test methods

Advanced nanomechanical testing has been used to evaluate key factors influencing tool life (1) a plasticity index (PI, the plastic work done/total work done during indentation), at room and elevated temperature (2) hot hardness and (3) fatigue fracture resistance, and determine their relative importance in different cutting applications. The optimum combination of hardness and toughness/plasticity to minimise wear and extend the life of coated WC–Co cutting tools was found to vary with the severity and nature of the cutting conditions. For interrupted cutting the plasticity index is critical, with high values (i.e. not extremely high H/ E) resulting in extended tool life. Elevated temperature nanoindentation showed decreasing hardness and increasing PI with temperature. In high-speed turning hot hardness is the dominant factor whilst for interrupted cutting high hot hardness should be combined with improved plasticity for longer tool life. A novel test technique nano-impact, was used to simulate the interrupted contact (and cyclic loading) conditions occurring in milling applications and evaluate the fatigue fracture resistance of coated tools. It was able to successfully rank coatings in terms of tool life in end milling and reproduce the evolution of tool wear in the cutting test. In elevated temperature nano-impact testing the probability and extent of fracture during the test decreased at elevated temperature, consistent with the higher PI. Results from the advanced nanomechanical tests can be used in combination to predict which coatings have longer life in severe cutting conditions.

Microstructure and mechanical properties of Ni–P coated Si 3N 4 reinforced Al6061 composites

Silicon nitride is currently a popular choice as reinforcement to develop light alloy composites owing to its high hot hardness and excellent wear and corrosion resistance. However, meager information is available as regards the development of aluminum alloy–silicon nitride composites by stir cast technique. This route of processing metal matrix composites (MMCs) poses challenges in particular, poor wettability of the ceramic reinforcement in the matrix alloy. To overcome this problem, researchers are currently focusing on use of metallic coated ceramic reinforcement. In the light of the above, this paper discusses the development of Ni–P coated silicon nitride reinforced Al6061 composites by stir cast method. XRD, metallographic, EDAX studies, microhardness, and tensile strength tests of the developed composites have been carried out. A maximum of 10 wt% of Ni–P coated silicon nitride has been dispersed uniformly in the matrix alloy. A drastic improvement in both microhardness and tensile strength is observed.

Deposition of Oxides as Tool Protection for Large Thixoforming Dies by Using the Pulsed MSIP-PVD Process

Oxide coatings offer great potential for their use in forming operations in the semi-solid state. Advantages of these types of coatings are high resistance against abrasive wear, high hot hardness and low thermal conductivity. Nevertheless deposition by pulsed Magnetron Sputter Ion Plating-PVD for oxide coatings is quite challenging: deposition rates are low and insulating layers on the target surface can cause arcing. On laboratory scale it was possible to deposit γ-Alumina using PVD in a temperature range, where hot working steel can be utilized. The next important step in the development towards an industrial application for larger forming tools is the upscaling process to larger coating units. In this work the process development of oxide coatings on an industrial coating unit for large tools was described. To increase adhesion of oxide top-layer additional bond coats were applied. Different process parameters like oxygen content, total pressure and substrate bias were varied, to improve the performance. The relationship between coating properties and process parameters of the deposited films were characterized by X-Ray-diffraction, Nanoindentation and Scanning Electron Microscopy (SEM). By using reactive pulsed PVD-process it was possible to deposit γ-Al2O3 on large steel tools for semi-solid melt protection. The developed coatings showed for thixoforging processes of X210CrW12 an extraordinary stability in field tests. The lifetime of the permanent moulds was increased by using PVD thin film coatings as a tool protection.

DURATECH XTREME

Abstract DuraTech Xtreme has very high impact toughness, high hot hardness, and good wear resistance. As indicated in the name, the alloy is intended for use in extreme” conditions. This datasheet provides information on composition, physical properties, hardness, and elasticity as well as fracture toughness. It also includes information on wear resistance as well as heat treating, machining, and powder metal forms. Filing Code: TS-663. Producer or source: Latrobe Specialty Steel Company.

Pulsed Nanocomposite TiAlN Coatings on Complex Shaped Tools for High Performance Cutting Operations

The demand on high profitability in cutting operations has led to a variety of requirements for high performance tool coatings. Nanostructured coatings have shown most promising results in this connection. High oxidation resistance, hot hardness, and loW friction are just a few benefits that these coatings offer. The deposition of nanostructured coatings is only possible within a small deposition process window. Most cutting tool surfaces are complex shaped and include, for instance, small corner radii at the cutting edge or chip breakers. The local process window and the deposition parameters must be adapted to the actual shape of the cutting tools in order to obtain a hard nanocomposite coating with adequate adhesion properties. Finally, the performance of these coatings has been studied in machining tests.

New approaches to plasma enhanced sputtering of advanced hard coatings

PVD coatings and cutting tool materials experienced a rapid development in the past due to the increased demands of modern, innovative HPC (High Performance Cutting) production processes. The development of new materials progressed so rapidly that it is partly not known, how these materials can be economically processed with respect to measures of reducing costs and thus increasing productivity. In order to meet the different requirements a range of developments have been brought forward in the area of coating technology. Al 2O 3 was and still is an important component of conventional coatings. Especially the different crystalline modifications synthesized by CVD have gained considerable economic significance. Distinct chemical resistance, higher hot hardness and less interaction with almost all production relevant materials than most hard coatings are the main success factors of Al 2O 3 films. Within the first step the plasma enhanced PVD technology for the deposition of ternary coatings with higher aluminum content was developed. These films continuously generate a protective crystalline alumina layer at elevated temperatures. In addition to RF- and DC-sputter sources, pulsed plasma sources are gaining increased attention in sputter technology. This interest is driven by the significantly enhanced ionization of pulsed plasmas as compared to conventional DC and RF techniques. Using highly ionized plasmas the High Ionization Sputtering (H.I.S.) and the High Ionization Pulsing (H.I.P.) processes have been developed to deposit a novel grade of high performance hard coatings, the supernitrides. The present paper provides a survey of latest approaches to plasma enhanced sputtering and related coating systems, with regard to the demands of high performance applications.

Capabilities of Cermets Tools for High Speed Machining of Austenitic Stainless Steel

Cermets tools have very high hot hardness together with a low coefficient of friction, which facilitates machining at high speeds. In the present work cermet tools coated with titanium nitride were used to turn austenitic stainless steel at speeds between 300 and 700 m min-1. Feed rates were varied between 0.05 to 0.4 mm rev-1. Depth of cuts were between 0.1 and 0.5 mm. After machining, tool flank wear and the cutting edges were observed using Scanning Electron Microscope (SEM). The experimental results showed that when cermet inserts were used for finishing cuts, very fine surfaces were produced. However, when used for roughing cuts, they tended to fracture unpredictably rather than having gradual flank wear. Thus, the cermet tools were found to perform satisfactorily only for finishing operations with feed rates ranging between 0.1 and 0.2 mm rev-1 and at the maximum depth of cut of 0.3 mm. For stable operations, the maximum cutting speed should be below 600 m min-1; exceeding this limit resulted catastrophic failure of the cutting edge.