The Detailed Microstucture of Primary Materials

A Full Laboratory Report on:

The Detailed Microstucture of Primary Materials

This report presents a study on the microstructure of 8 material samples using the proper optical microscopy techniques. Emphasis is given in sample preparation, the right use of transmitting and reflecting optical microscopy methods, and a detailed analysis of the distinct microstructure of metal, ceramic, and polymer materials. For metals and ceramics, preparation procedures include grinding, polishing, and surface treatment (etching) which may vary in different samples. Generally, for opaque materials as such, the samples are viewed in reflecting mode. In the case of polymers, samples are sliced into very thin layers for viewing in transmitting mode, due to their translucent properties to light. This technique utilizes principles in the polarization of light to obtain distinct elements of the microstructure. The microstructure of metals and ceramic binary alloys can be accurately interpreted using the information provided in their respective phase diagrams (eutectic and binary), which explains the outcome of the microstructure based on previous heat treatment and alloy composition. It has also been observed that alloys with similar composition, but prepared under dissimilar heat treatment conditions possess stark differences in grain structure and phases present. As for polymers, differences in microstructure can be attributed to their crystalline and non-crystalline properties.

I. Background of Study

The study of the microstructure of materials is of great significance as many of the final physical and mechanical properties depend on it. In this report, we narrow our focus to the different microstructures in metallic, ceramic, and polymeric materials. Because the features that exist in the material surfaces are unclearly distinguished by the unaided eye, electron and optical microscopy are generally the methods used in determining microstructure, and for our purposes, we will utilize transmitting and reflecting microscopy to investigate the internal structure of the materials at hand. This is to enable us to observe the specimen at a wider surface area and at lower magnifications in the air, so as to determine the general features in the surface needed for our analysis.

The procedure and details in sample preparation before microscopic observation is detailed in the following sections as careful and appropriate surface treatments are needed to uncover the important details in studying the microstructure. Generally, metals and ceramics are treated quite similarly, and polymer samples are prepared in a different way to suit the microscopic technique used in observation. The reflecting light microscope is employed in studying metals, ceramics and some polymers which are opaque by nature, relying on the reflectance properties of individual grains to determine its texture. On the other hand, transmitting light microscopes are used in polymeric substances that allow light to pass through the sample when prepared adequately through a microtome slicing technique.

The analysis of the material's surface structure in metals and ceramics are primarily carried out through careful interpretation of its corresponding phase diagram, which provides a relation between alloy concentration, temperature, and the corresponding phases and amounts that form in distinct regions at constant pressure. It is also important to keep in mind that phase diagrams only convey the equilibrium transformations that occur in varying temperatures, which is highly dependent on time factors, such as cooling rate (Callister, 2003). Polymer microstructure is generally analyzed by comparing the similarities and differences expressed in crystalline and non-crystalline polymer samples studied in the experiment.

The study of the microstructure of common materials such as steel (Fe-C alloy), epoxy, polypropylene, and zirconia contribute more to deepen our understanding to their respective properties leading to their industrial applications which contribute to improve and uphold the standards of our everyday lives.

II. Objectives of the Experiment

The primary objectives of this exercise is to know the necessary procedures and methods in using the optical microscope to view the microstructure of select materials and to study the various types of microstructures inherent in these materials and to identify them accordingly.

III. Equipment and Materials Used

The samples evaluated in this experiment are of metallic, ceramic, and polymeric nature and are indicated as follows in Table 1.1

Material Type Specimen Index Heat Treatment Conditions

Metal X14 Al-4% Cu alloy, rapid cooling from 525 Ñ"C

Metal X15 As X14, reheat specimen at 260 Ñ"C for 70hours

Metal X17 0.8%C steel, furnace cooling from 800 Ñ"C

Metal X19 0.35%C steel, furnace cooling from 870 Ñ"C

Metal X25 0.35%C steel, water quenched from 870 Ñ"C

Ceramic Zirconia Dry Pressing and sintering

Polymer Polypropylene (PP) No heat treatment

Polymer Epoxy No heat treatment

Table 3.1 - Different material types observed in this experiment

The equipment used in the exercise is briefly summarized in Table 3.2

Equipment Stage Used Description

Abrasive cut-off machine Sample Prep. Employed in grinding process for metals and ceramics

Hand Grinder Sample Prep. Employed in grinding process for metals and ceramics

Automatic Polisher Sample Prep. Used to polish metals and ceramics to mirror-like finish.

Universal Polisher (twin) Sample Prep. Used to polish metals and ceramics to mirror-like finish.

Microtome Sample Prep Slices polymer sample to very thin layers

Reflective Light Microscope Examination Microscopic observation used for metals and ceramics