Machinable Glass Ceramics

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Machinable Glass Ceramics

Transcript of Machinable Glass Ceramics

Composition, Microstructure, Properties of Machinable Glass CeramicsMMS 802 Ph.D Seminar report Submitted in partial fulfillment of the requirements of the degree of Doctor of philosophy By

HARSHAVARDHANA.N Roll.No: 10411413Under the guidance of

Prof. PARAG BHARGAVA(Department of Metallurgical Engineering and Materials Science)

Department of Metallurgical Engineering and Materials ScienceINDIAN INSTITUTE OF TECHNOLOGY BOMBAY 31March, 2011

CONTENTS

List of Figures List of Tables Nomenclatures

i ii iii

Chapter 1. Introduction1.1 1.2 1.3 1.4 1.5 Definition Glass-ceramics Machinability of Glass Ceramics Advantages Machinable Glass ceramics Application of machinable glass ceramics

1 1 1 3 3 4 5 5 7 7 11 13 18 21 23

Chapter 2 Literature Survey2.1 2.2 2.3 2.4 2.5 2.6 Background of Invention Composition of Machinable glass-ceramics Preparation of Machinable glass-ceramics Properties of machinable glass ceramics Microstructure Study of Machinable Glass Ceramics Machinability of Machinable Glass Ceramics

Chapter 3 Summary References

List of Figures 1) 2) 3) 4) 5) 6) 7) 8) 9) 10) 11) Components from machinable glass ceramics Heat treatment cycle for glass ceramics Heat treatment cycle for a machinable glass-ceramic material DTA diagram of the base glass 1 2 8 8

Schematic flow diagram of heat treatment process for machinable glass-ceramic 9 Crystal Structure of glass-ceramics at 586C after 5 minutes Crystal Structure of glass-ceramics at 910Cafter 5 minutes Crystal Structure of glass-ceramics at 940C after 5 minutes Crystal Structure of glass-ceramics at 950C Microstructure of machinable glass-ceramic by SEM and TEM X-ray diffraction pattern of machinable glass-ceramics at various temperature range. 14 9 10 10 10 13

12)

X-ray diffraction pattern of machinable glass-ceramics subjected to heat treatment 15

13)

Microstructure and Energy Dispersed X-ray analysis of machinable glass-ceramics. 15 16 17 17 17 18 Microstructure at 650oC after 1 hr of heating Microstructure at 750oC after 1 hr of heating Microstructure at 850oC after 1 hr of heating Microstructure at 950 C Microstructure of machinable glass ceramics with high aspect ratio Tool wear vs Time of machining for machinable glass ceramics for turning operation 20o

14) 15) 16) 17) 18) 19)

i

List of Tables

1. Composition of Machinable glass-ceramics 2. Mechanical Properties 3. Thermal Properties

7 11 12 12

4. Electrical Properties

ii

Nomenclatures

Si K B Mg DTA XRD EDX TEM SEM

Silicon Potassium Boron Magnesium Differential Thermal Analysis X-ray Diffraction Energy Dispersed X-Ray Diffraction Transmission Electron Microscope Scanning Electron Microscope

iii

Composition, Microstructure, Properties of Machinable Glass Ceramics Chapter-1: Introduction

1.1. Definition:Machinable glass-ceramics is a white, opaque polycrystalline materials formed by the controlled crystallization of glass. These glass ceramics can be easily machined into desired shape using standard metalworking tools. [1] Glass Ceramics + Machinability = Machinable glass-ceramics

Figure 1: Components from Machinable Glass Ceramics [2]

1.2. Glass-ceramics:The glass-ceramics are the polycrystalline materials formed by controlled crystallization of glass It exhibits both the properties glasses and ceramics. These glassceramics are produced by controlled crystallization process which results in exhibiting both amorphous and crystalline phases.[1] The production of glass-ceramics involves two main steps. .In the first stage of heat treatment process, the batch is melted at 1700oC which results in formation of transparent glass. During second stage of heat treatment, the glass-ceramics is produced by heating the glass to a temperature range of 530oC to 760oC for the considerable period of time of about 8 hrs, which results in nucleation of crystals and followed by heat treatment to a temperature1

range of 850oC to 1100oC for about 3 hrs, which results in the formation of randomly oriented glass-crystals.. Thus by the end of this process, partly crystallized glass ceramics structure is formed which has the application in many field. [1]

Fig 2:Heat treatment cycle for glass ceramics [3]

General properties of Glass ceramics are as follows [3]

Odourless, opaque white material High temperature resistance Non-porous Dimensionally stable Good insulator

A wide variety of glass-ceramic which are widely used are as follows [4] Li2O x Al2O3 x nSiO2-System (LAS-System), MgO x Al2O3 x nSiO2-System (MAS-System), ZnO x Al2O3 x nSiO2-System (ZAS-System), Glass-ceramics made of Lithium-Disilicate and Machinable glass-ceramics

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1.3. Machinability of Glass Ceramics:Machinability is defined as the ability of the material to machine easily with the acceptable level of surface finish and depth of cut. Machinability is difficult to predict as it involves many variables such as microstructure of the materials, grain size, heat treatment, chemical composition, fabrication method, hardness, yield strength, of the materials, tensile strength of the materials etc. Further it dependents on the physical conditions such as modulus of elasticity, thermal conductivity, thermal expansion, and work hardening. [5] The machinability of material can be predicted based in the following methods a) Tool life method: Machinability of material can be predicted by measuring amount of wear on the tool for the constant depth of cut and surface roughness. b) Tool forces and power consumption method Machinability of material can be predicted by calculating the total force and total power consumption acting on the material for the constant depth of cut and surface roughness. c) Surface finish method Machinability of material can be predicted by measuring surface roughness value for the desire depth of cut and tool.[5]

1.4. Advantages Machinable Glass ceramics It can operate at continuous usable temperature of 800 C and with a peak temperature of 1000 C. It is a low thermal conductivity and a good thermal insulator even at very high temperatures It also act as an excellent electrical insulator Machinable glass ceramics is porous-free material and does not outgas when baked out. This makes the machinable glass ceramics as an ideal material for ultrahigh vacuum applications.

3

It has a very high strength, rigidity and creep limit. It is radiation-resistant and is therefore used in nuclear engineering. Machinable glass ceramics has a property to join or sealed to itself or other materials in a number of ways through metallizing, brazing, fritting or using epoxy resin.

It is white and can be bright-polished. Thus it is used in medical and optical devices. [4,6,7]

1.5. Application of machinable glass ceramics:Machinable Glass ceramics can be widely used in following areas [4,6,7]

Flight and aerospace applications Used as spacers, headers and windows for microwave tube devices Used as substrates for Field Ion Microscopes Used in welding nozzles Medical equipments. Sample holder for microscope Sealing glass. High temperature applications Used in stove windows, cookware and tableware etc

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Chapter-2 - Literature Survey

2.1. Background of InventionSazmal (2008) et al have worked in crystallization and microstructural evolution of commercial fluosilicate glass-ceramic in which the glass ceramics is characterized by using advanced microscopy techniques. Further the microstructural characteristics and crystal evolution based on melting, heat treatment and phase transformation of crystal was studied in this journal.[11]

Denry1 (1999) et al have worked in preparation and characterization of a new lithium-containing glass-ceramic in which he has compare the thermal properties and microstructure of a new lithium-containing glass-ceramic to a experimental dental glass ceramic. The chemical composition of both control and experimental glasses was determined by electron microprobe analysis. The nucleation and crystallization temperatures were determined by Differential Thermal Analysis (DTA). The glass specimens were submitted to various heat treatments and analyzed by X-ray diffraction (XRD). Thus the results showed that optimal crystallization of the experimental glass-ceramic was achieved after heat treatment at 950C for 30 min. Further it is observed that the microstructure of the experimental glass-ceramic exhibited mica platelets randomly oriented and highly interlocked.[16]

Balk et al (1995) have worked in comparative evaluation method of machinability for mica-based glass-ceramics and machinability of mica glass-ceramics is evaluated using a tool dynamometer. Several samples with different chemical compositions and microstructures were tested in turning operations using TiCN cermet tools. Thus the cutting rate has been studied to for the evaluation of machinability. The mechanical strength, surface roughness and fracture toughness were measured to support the machining behavior.[17]

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Saraswati et al (1992) have worked on glassed ceramics with K20-MgO-AI2O3MgF2-SiO2 composition through the sol-gel. Thus the resultant powder produced after heat treatment is hot pressed into workable discs. Thus the glass-ceramic was found to be machinable with conventional tools. Its physical and mechanical property is compare with commercial macor and it is tabulated. Further the microstructure study is also made to analyze the flexure strength of the given machinable glass ceramics.[15]

Toshio Hamasaki et al (1988) have worked on prepartion and characterized machinable mica glass ceramics by Sol-gel process. The physical, chemical, electrical and mechanical pro