Ark PVD yöntemiyle tin kaplanmış kesici takımların karakterizasyonu ve performanslarının incelenmesi
Başlık çevirisi mevcut değil.
- Tez No: 66677
- Danışmanlar: PROF. DR. E. SABRİ KAYALI
- Tez Türü: Yüksek Lisans
- Konular: Metalurji Mühendisliği, Metallurgical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1997
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Metalurji Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Malzeme Bilim Dalı
- Sayfa Sayısı: 225
Özet
ÖZET Talaş kaldırma işlemlerinde kullanılan kesici takımların aşınma sonucu sınırlanan ömürleri, talaşlı imalat proseslerinin toplam maliyeti üzerinde önemli etkiye sahiptir. Takım ömrünün arttırılması, talaş kaldırma işleminin maliyetini önemli oranda azaltmakta, işlemin verimliliğini ve üretim hızını da arttırmaktadır. Kesici takım yüzeylerinin ince, sert seramik filmlerle kaplanması ile takım ömrü arttırılmakta ve yukarıda söz edilen amaçlara ulaşılabilmektedir. Sert seramik kaplamaların takım yüzeylerine başarıyla yapılabildiği yöntemlerden bir tanesi Fiziksel Buhar Biriktirme (PVD) tekniğidir. Bu teknik, vakum altında bulundurulan malzemelerin buharlaştırılarak veya sıçratılarak atomların yüzeyden kopartılması ve kaplama yapılacak yüzeye atomsal veya iyonsal olarak biriktirilmesi esasına dayanır. Bu çalışmada kullanılan kesici takımların bir kısmına PVD katodik ark buharlaştırma tekniğiyle TİN kaplanmış, diğerleri kaplamasız olarak kullanılmıştır. İTÜ Kimya-Metalurji fakültesi kaplama karakterizasyon laboratuvarında, kesici takımların kaplama kalınlıklarının, yüzey pürüzlülüklerinin, sertliklerinin ve taban malzemeye yapışmalarının belirlenmesi amacıyla çeşitli karakterizasyon çalışmaları yapılmıştır. Performans deneyleri, Makina Takım Endüstrisi A.Ş. ve Türk Elektrik Endüstrisi A.Ş. tesislerinde GG-25 dökme demir iş parçasına karşı yapılmıştır. Performans deneylerinde, 0,4 mm. serbest yüzey aşınma şerit genişliğine ulaşıncaya kadar takımın katettiği toplam kesme mesafesi aşınma kriteri olarak kabul edilmiştir. Çalışmalar sırasında DİN 1.3343 yüksek hız çeliği, DİN 1.3243 yüksek hız çeliği ve TİN kaplanmış DİN 1.3243 yüksek hız çeliği takımlar kullanılmış ve kesme performansları karşılaştırılmıştır. Ayrıca farklı kaplama parametreleri kullanılarak kaplanmış ve aynı kesme koşullarında kullanılmış takımların kesme performansını inceleyen bir başka çalışma referans olarak alınarak, kaplama proses parametrelerinin ve kaplama özelliklerinin takım ömrüne etkileri incelenmiştir. Çalışmalar sonucunda, TiN kaplanmış DİN 1.3243 takımların, kaplanmamış DİN 1.3243 ve DİN 1.3343 takımlardan daha yüksek takım ömrüne sahip oldukları anlaşılmıştır. TiN kaplanmış DİN 1.3243 takımlar, kaplanmamış DİN 1.3243 takımlardan ortalama 2 kat, kaplanmamış DİN 1.3343 takımlardan ise ortalama 4 kat daha uzun takım ömrü sergilemişlerdir. Ayrıca daha düşük taban malzeme yüzey pürüzlülüğüne, daha düşük kaplama kalınlığına, daha yüksek sertliğe sahip olan ve taban malzemeye yapışması daha iyi olan takımların aşınma direncinin de daha yüksek olduğu anlaşılmıştır. Xİİ
Özet (Çeviri)
SUMMARY Tribology can be defined as the study of the science and technology of interacting surfaces in relative motion. This term can be divided into three subjects. These are“friction”, lubrication“ and ”wear“. Wear can be defined as the material loss due to material transfer from one to another surfaces which are in contact. Wear is typically effected by the material geometry, material hardness and environment condition. Wear can be separated into four general type; adhesive wear, abrasive wear, corrosion wear and surface fatique. Adhesive wear processes are initiated by the interfacial adhesive junctions that form if solid materials are in contact on an atomic scale. As a normal load is applied, local pressure at the asperities becomes extremely high. In some cases, the yield stress is exceeded, and the asperities deform plastically until the real area of contact has increased sufficiently to support the applied load. In the absence of surface films, the surfaces would adhere together, but very small amounts of contaminant minimize or even prevent adhesion under purely normal loading. Abrasive wear occurs in contacts where one of the surfaces is considerably harder than the other or where hard particles are itroduce into the contact. The harder surface asperities are pressed into the softer surface which results in plastic flow of the softer material around the hard one. When the harder surface moves tangentially, ploughing and removal of softer material takes place with grooves or scratches in the surface resulting. Wear shortenes the tool life in machining processes such as drilling, tapping, reaming, turning and milling. Wear of the tool materials creates an extra cost in machining processes. Cutting tools wear because normal loads on the wear surfaces are high and the cutting chips and the workpiece which apply these loads are moving rapidly over the tools wear surfaces. The cutting action at related friction at these contact surfaces increase the temperature of the tool material which accelerates the physical and chemical processes associated with tool wear. Therefore, cutting tool wear is an economic penalty that must be accounted for in order to machine the part. Four main mechanisms of tool wear have been identified, namely adhesive wear, abrasive wear, delamination wear and wear due to chemical instability, including diffusion, solution and electrochemical wear. In addition, there are some wear modes on tools. They are flank wear, crater wear and built up edge. Flank wear is believed to be caused mainly by abrasion of the tool by hard particles but there may be adhesive effects also. It is the dominating wear mode at low cutting speeds. Crater wear is the formation of a groove or a crater on the tool face, typically some 0,2-0,5 mm. from the cutting edge, at the place where the chip moves over the tool surface. XXIIIIt is very commonly observed when cutting high melting point metals like steel at relatively high cutting speeds. Crater wear is caused primarily by the dissolution of tool material by diffusion or solution wear since it occurs in the region of maximum temperature rise. Built-up edge of piled up work material near the tip of the cutting edge is frequently formed at intermediate cutting speeds. The built-up edge is often unstable; it breaks away intermittently and is formed again. Depending on the materials and cutting conditions the influence of the built up edge may sometimes decrease or at other times increase the tool life. A stable built up edge can be beneficial and protect the tool surface from wear. On the other hand loose highly strain-hardened fragments of the built-up edge may adhere to the chip or workpiece and cause abrasion of the tool. At higher cutting speeds a built-up edge is less likely to form because the temperature increases and the built-up edge can no longer support the stress of cutting and will thus be replaced by a flow zone. The wear of the cutting tools takes place in three stages. In the initial wear stage the two materials in contact have surface roughness irregularities in the form of protrusions or asperities. At the interface, asperities from the two materials touch, defining tiny contact areas. The total area from these contact points is a fraction of the projected area of the contact surface. The stresses and heat are intensify in the asperities and partial removal may occur due to seizure accompanied by fracture of the asperity or melting in the asperity. As these asperities are removed, the initial surface roughness is altered and the contact area increases. If the force conditions remain unchanged the pressure decreases and the active wear mechanisms change to plasticity and/ or mild oxidation/ diffusion- dominated wear. This initial wear period will create small, visible wear surfaces. A velocity and normal stress condition that would continue to cause seizure and melt should be avoided because it would soon cause complete failure of the cutting tool. Assuming that such conditions do not exist, the wear surfaces will get progressively larger. If plasticity dominated small particles of material are mechanically deformed and fracture away from wear surface. This is generally called abrasion and can occur on any of the wear surfaces; it is the most common wear process along the clearance or flank surfaces of most tools. As discussed earlier, normal stress and temperature very over the wear surfaces so that a plasticity mechanism that dominates in one wear zone may not dominate in another. The cutting tool is only one element of the machining system. This is a complex system consisting of the workpiece, the workpiece holding fixture, the tool holder, the machine tool and the cutting fluid system. Also more complex cutting tool geometries are no available that control chip motion or chip breakage such that the process is more productive and the wear rate of tool reduce. When configuring a machining system, the selection process starts by obtaining knowledge about the type and quality of the surfaces to be machined. The selection of the machine tool depends upon the sequence of surface types that will be used, the quality of each of these surfaces, and machining capacity needed for each of these surfaces. XXIVTool materials need to be wear resistant, tough and have a characteristic referred to as hot hardness. Wear resistance is the ability of the material to have a useful life when subjected to the types of wear mechanisms. Toughness is needed so that the cutting edge will not chip or fracture, particularly when subjected to impact loads. Tough materials can absorb energy and resist plastic deformation without fracturing. Hot hardness is the ability of the material to maintain hardness at elevated temperatures. Recovery hardness is the ability of the material to regain hardness at room temperature, after being subjected tool an elevated temperature. During metal cutting, temperature on the rake face of tool can be so high that cutting tools atoms diffuse through chip and material loss from the rake face of tool takes place. High technology today demands combinations of diverse properties from a material which is generally unobtainable from a single or monolithic material. Coating technology has advanced rapidly in the past twenty years and it has greatly assisted in meeting such complex demands placed on materials. The important coating methods for high technology applications are plasma and detonation gun spraying techniques, electrodeposition, chemical vapor deposition (CVD), and physical vapor deposition processes. Chemical vapor deposition is generally defined as the deposition of a solid material on tool onto a heated substrate as a result of chemical reactions in the gas phase. These reactions may occur on, at, or near the substrate surface. On the other hand, physical vapor deposition processes which are originally applied to the deposition of single materials. Such as metals did not involve chemical reactions. The versality of the PVD processes lead to the development of PVD processes. For the deposition of compounds which necessarily involve chemical reactions. Thus, the distinction between CVD and PVD processes becomes less sharp. PVD technology consists of the techniques of evaporation, ion plating and sputtering. It is used to deposit films and coatings or self supported shapes such as sheet, foil, tubing, etc. The thickness of the deposits can vary over a wide variety of applications from decorative to utilitarian over significant segments of the engineering, chemical, nuclear, micro electronics and related industries. Many different coatings such as nitrides, carbides and oxides are used to enhance the performance of cutting tools. Commonly applied coating materials include titanium nitride (TiN), titanium carbide (TiC) and aluminum oxide (A1203); these coatings are usually deposited in a single or multilayer manner onto the tools by chemical or physical vapor deposition techniques. The popularity of CVD and PVD stems from the fact that the deposited coatings can improve the wear resistance significantly without effecting tool dimensions as compared to some other coating techniques. XXVHowever, many research studies had already shown in the mid 1980's that with ternary hard materials, e.g. titanium carbo nitride (TiCN) or TiAlN. TiCN can be characterized by a higher hardness and better abrasion resistance compare to TiN. TiAlN also posses a higher hardness compared to TiN however TiAlN has a lower heat conductivity and friction coefficient in contrast with TiCN. TiAlN shows a higher strength at elevated temperature, a higher oxidation resistance and better thermal barrier properties compared to TiN Properties of coatings can be determined by coating characterization techniques. The main coating characterization parameters for triboelements are; ? Coating thickness ? Coating surface roughness ? Coating hardness ? Coating adhesion to substrates. The adhesion of characterised by means of a newly developed scratch analyzer, equipped with a Rockwell C diamond stylus of tip radius D=200 micron. In a fully computer controlled experiment, the actual values of the normal load, the frictional force and the acustic emission are recorded simultaneously. While the load on the scratch diamond tip is linearly increasing. Coating thickness analyses are generally carried out using the ball created method, where the coating thickness is determined from the dimension of the spherical creater produce on the coating surface. Also ultra micro hardness testing is used for coating hardness measurements. Restricted tool lives of the cutting tools used in machining processes due to tool wear have got an important effect on the total cost of machining processes. To enhance the tool life decreases the cost of machining processes considerably and increases the productivity as well. These purposes can be reached by depositing thin, hard ceramic coatings onto cutting tool surfaces. One of the commercially usable and successfully applied techniques by which hard ceramic coatings can be deposited onto tool surfaces is Physically Vapour Deposition (PVD) technology. In this technique, materials in a vacuum environment are evaporated or sputtered in order to break off the atoms from the material surface and are deposited onto the tool surface in atomic or ionic manner. In this study,the effects of TiN coatings on the tool lives of several cutting tools are investigated. HSS (DIN 1.3343) and approximately 5% Cobalt alloyed HSS (DIN 1.3243) twist drills, taps and reamers produced in different shapes and dimensions were tested. Their geometries and compositions are given below. All of the cutting tools are exposed to heat treatments to increase their hardnesses. Some of the cobalt added tools (DIN 1.3243) were coated with TiN by Cathodic Arc Evaporation PVD technique. These tools which were uncoated and TiN coated conditions experiment. Various characterization tests were made in Ystanbul Technical University, Coating Characterization Laboratories to measure the surface roughnesses (before and after coating process), coating thicknesses, coating XXVIhardnesses and adhesion strengths of the coatings to the tools (substrates). After that, performance tests of the cutting tools were made in Turkish Electrical Industry (TEEA5) and Machine & Tool Industry (MTEA>) in normally production conditions to prove the wear resistance and tool lives of TiN coated and uncoated cutting tools during the machining of GG25 gray cast iron workpieces. In performance tests, the cutting tools used in this study were uncoated and coated conditions. The total cutting distance of the tools until the amount of flank wear (VB) reaches to 0,4 mm. Was accepted as the wear criterion. During the tests, performance and wear resistance of uncoated DIN 1.3343, uncoated DIN 1.3243 and TiN coated DIN 1.3243 tools were compared to each others. In addition, performance and wear resistance of TiN coated DIN 1.3243 tools were compared with the other TiN coated DIN 1.3243 tools coated by using different process conditions, but proved in the same conditions. Therefore the effects of coating process parameters and coating characteristics on the tool lives were determined. In heat treatments, all of the cutting tools were annealed at 1200°C for 20 seconds per each mm. diameter of tools; then they were tempered four times. First and second tempering treatments were performed at 550°C for 90 minutes; third and fourth ones were performed at 550°C and 540°C respectively for 60 minutes. The hardnesses of the cutting tools after heat treatments were in the range of 882-920 HV. Workpieces used in performance tests were GG25 gray cast iron with a composition of 3,2-3,5% C, 2,1-2,4% Si, 0,6-0,9% Mn, 0,074% S and 0,042% P. Their hardnesses were in the range of 180-240 HB. Surface roughness measurements of the cutting tools were performed by using Perthometer S8P type mechanical profilometer. Surface roughnesses of the tools were measured before and after coating. Ra parameter was selected as the measure of surface roughness. It was seen that average surface roughness after coating process had increased about 0,05 urn. compared to that of before coating process. XXVIICoating thicknesses were measured by ball cratering method by using Wirtz Buehler Calotest apparatus. Surfaces of the coated tools were abraded by rotating a steel ball with 10 mm. diameter with a rotating velocity of 1800 RPM for 20 seconds. 1 urn. diamond suspension was added into coating and ball interface. It was seen that, coating thicknesses of the coated tools had varied in the range of 1,45-2,55 urn. Coating hardness measurements were performed by Using Fischerscope HP 100 XYPROG micro hardness apparatus. All of the measurements were taken under load and application loads were such selected that indentation depth couldn't excess 10% of coating thickness for each tool. Loads were applied with 0,1 second interval in 50 stages. It was seen that coating hardnesses had varied in the range of 2000-3400 HV. Measurements of adhesion between coating and tool material were performed by using IPA Stratch Tester. Maximum load and loading distance were selected 130 N. And 100 N/minute respectively in the test. Stratch test results showed that Leu critical loads of the tools were in the range of 23-33 N. and Lc2 critical loads were in the range of 90-1 35 N. Performance tests were performed by using DIN 1.3343, uncoated DIN 1.3243, and TiN coated DIN 1.3243 HSS tools in normal operation conditions. When the amount of flank wear (VB) reached to 0,4 mm., the test was stopped and total cutting distance (number of the parts x cut depth) was measured. Bortex 5% emulsion was used in the tests as the cutting fluid. All of the cutting tools were divided into four different cutting velocity. They could be sorted as 1 1,05±8% m/min (taps), 15,15 m/min. (reamers), 26,17±15% m/min. (twist drills), and 36,47±11% m/min. (twist drills). Each group contained tools which had got different cutting forces; so general evaluations were made due to cutting forces and velocities i.e. it was tried to determine that how cutting forces and velocities of the tools effect the wear resistance and tool lives. In addition, the effects of TiN coating and Co content onto tool lives were determined. It was seen that uncoated DIN 1.3243 (with 5% Co content) had exhibited approximately 2 times longer tool lives than that of uncoated DIN 1.3343 (without Co content) tools and also seen that TiN coated DIN 1.3243 tools had exhibited 4 times longer tool lives than that of uncoated DIN 1.3343 ones. DIN 1.3243 tools exhibited more tool lives than DIN 1.3343 ones because of their Co content. Cobalt inhibits the growth of grains at elevated temperatures and so increases the high temperature performance of the tools. Cutting forces and cutting velocities effected the tool lives as well. Generally it was shown that tool lives had decreased by increasing cutting velocities and cutting forces. For example at low cutting velocities such as 11,05±8% m/min., total cutting distances for TiN coated tools were more than 100000 mm., however at high cutting velocities such as 36,47±1 1%, total cutting distances for TiN coated tools were lower than 50000 mm. Cutting forces had the same effect as that of cutting velocities i.e. the total tool lives decreased due to increase of cutting forces. XXVIIIThe proportional tool lives of TiN coated DIN 1.3243 tools relative to uncoated DIN 1.3343 tools were increased at high cutting velocities and cutting forces i.e. TiN coated DIN 1.3243 tools exhibited better performance relative to uncoated DIN 1.3343 tools at high cutting velocities and forces. This can be summarized that TiN coated tools exhibited better cutting performance at severe cutting conditions because of the resistance of TiN coating to high temperature adhesive and abrasive wear. The results of tool lives for each tool are given below: TiN coatings resist the built-up edge formation or reduce the shape and dimensions of it. So at low cutting velocities and forces at which built-up edge formation mechanisms are effective, TiN coated tools showed higher tool lives than that of uncoated tools. Different process parameters used during coating process also affected the wear resistance and tool lives of the tools. Generally, tools which had smoother surfaces, higher coating hardnesses and better adherence of coatings to the substrates exhibited better cutting performance. As the result of microscopic observations of the tools used in performance tests, it was seen that adhesive wear was effective at lower cutting velocities and forces and inversely abrasive wear was effective at higher cutting velocities and forces. Wear of the tools didn't occur homogeneously rather occurred by spalling and cracking of the coatings. As a result of the economical analysis, it has been determined that although TiN coated tools were more expensive, tool cost per one part by using TiN coated tools reduced 26-84% compared to that of uncoated ones due to machining much more parts by one tool. The results of the present investigations are summarized below: XXIX1) The tool lives and wear resistance's of DIN 1.3243 quality high speed tool steel (HSS) which contain about 5% cobalt in their composition are higher than that of DIN 1.3343 quality cutting tools. The main effect of cobalt in HSS is to increase the hot hardness and thus to increase the cutting efficiency when high tool temperatures are attained during the cutting operation. The increasement observed in tool life of DIN 1.3243 quality HSS tools is about 2,2-4 times with respect to DIN 1.3343 as a function of tool type and cutting parameters (Cutting velocities and cutting forces). 2) DIN 1.3243 quality cutting tools were coated by TiN layer under the following conditions. Cleaning and heating conditions: Cleaning time: 10 minutes Cleaning bias; 1000 V, Cleaning temperature: 400°C Cleaning pressure: 8.10”6 mbar Coating conditions: Coating time: 1 hour Coating bias: 100-400 V. Coating temperature: 120-420 °C Nitrogen partial pressure: 1,6. 10"2 mbar The characterization of TiN coated tools exhibited that: Thickness: 1,6-2,5 urn. Hardness: 2026-3322 HV Roughness (Ra): 0,11-0,50 p,m. Critical load: 24-33 N. It is included that the hardness and the critical load which is the major of adhesion strength between substrate and coating decrease with increasing thickness. 3) TiN coatings deposited onto DIN 1.3243 quality HSS tools enhanced the tool lives and wear resistance's of the cutting tools significantly with respect to uncoated DIN 1.3243 and DIN 1.3343 quality HSS tools. TiN coatings deposited onto DIN 1.3243 quality HSS tools increased the tool lives about 2,2-4 times with respect to DIN 1.3343 quality HSS tools as a function of tool type and cutting parameters. 4) Microscopic examinations on the worn surfaces of TiN coated cutting tools reveal the failure mechanisms as coating spallation in many locations, the transfer of the work material to the tool surface where TiN coating was removed. Extensive wear was observed at flank faces and plastic deformation at cutting edges. XXX
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