Characterization of Aluminum-Boron Carbide Particulate Metal Matrix Composites Eric Blank 6/4/10 Senior Project Dr. London Approval Page Project Title: Characterization of Aluminum-Boron Carbide Particulate Metal Matrix Composites Author: Eric Blank Date Submitted: June 4, 2010 CAL POLY STATE UNIVERSITY Materials Engineering Department Since this project is a result of a class assignment, it has been graded and accepted as fulfillment of the course requirements. Acceptance does not imply technical accuracy or reliability. Any use of information in this report is done at the risk of the user. These risks may include catastrophic failure of the device or infringement of patent or copyright laws. The students and staff of Cal Poly State University, San Luis Obispo cannot be held liable for any misuse of the project. Prof. ____________________________ Faculty Advisor Signature Prof. Trevor Harding ____________________________ Department Chair Signature Abstract The analysis of die-cast 380 aluminum-boron carbide particulate metal matrix composites (MMC) was performed in order to see if the samples had the required tensile strength of 300 MPa. 10 wt% B 4C die-cast samples were produced and tested. Half were heat treated to the T6 condition and the others were left as cast. Using ASTM standard B 557M it was found that the average tensile strength for the as-cast samples was 130 MPa and the heat treated samples had a tensile strength of 93 MPa. These values were both lower than expected. The heat treated samples were not expected to have a lower tensile strength than the as-cast samples. Since hardness is related to tensile strength, microhardness values were obtained to see if there could be an explanation for the unpredicted tensile data. The non-heat treated samples had an average hardness of 114 HV while the heat treated samples had an average hardness of 123 HV. A two sample t-test failed to prove a significant difference in the microhardness values of the two separate treatments. With no conclusions being able to be drawn from the hardness data, metallographic samples of each treatment were produced to examine the microstructure of the material. Both samples showed that the B 4C particles were not homogeneously distributed; there were highly concentrated regions of B 4C particulates. In addition, both were highly porous. From this information, it was inferred that the weakness was due to fracture initiation at these regions. In order to gain the strength desired it will be necessary to have a more evenly dispersed reinforcement as well as reducing the porosity. Key Words: boron carbide, metal matrix composite, die-casting, aluminum, particulate, materials engineering List of Figures Figure 1 An aluminum silicon carbide component is used in wafer processing.............................. 2 Figure 2 Schematic of fiber production............................................................................................ 3 Figure 3 Diagram of die casting process......................................................................................... 4 Figure 4 Shear loading of discontinuous fibers ............................................................................... 6 Figure 5 Image of how particulates effect grain size. ...................................................................... 8 Figure 6 Correlation of hardness and tensile strength .................................................................... 8 Figure 7 Diagram of how samples were prepared for microscopy................................................ 11 Figure 8 Diagram of where samples were tested.......................................................................... 12 Figure 9 Picture of gravity cast specimens.................................................................................... 13 Figure 10 An AutoCad drawing of the tensile grips ....................................................................... 13 Figure 11 Picture of the die cast samples…………………………………………………………….. 15 Figure 12 5% B 4C microstructure .................................................................................................. 16 Figure 14 10% B 4C microstructure ................................................................................................ 17 Figure 15 15% B 4C microstructure ................................................................................................ 18 Figure 16 Sample of volume percent B 4C calculation. .................................................................. 19 Figure 17 Stress-strain chart of gravity cast samples. .................................................................. 20 Figure 18 Bar chart of maximum stress and elongation................................................................ 20 Figure 19 Stress-strain curve of as-cast samples. ........................................................................ 21 Figure 20 Stress-strain curve of 380 T6 heat treatment................................................................ 22 Figure 21 Stess-strain curve of A356 T6 heat treatment. ............................................................. 22 Figure 22 Comparison of fracture surfaces ................................................................................... 25 Figure 23 Fracture surface ............................................................................................................ 26 Figure 24 Void in the sample......................................................................................................... 26 Figure 25 Interior of a void............................................................................................................. 27 List of Tables Table I Average Volume Percent of Reinforcement...................................................................................... 19 Table II Average Calculated Volume Percentages........................................................................................ 19 Table III Average Tensile Strength................................................................................................................ 23 Table IV Average Strain................................................................................................................................ 23 Table V Average Hardness........................................................................................................................... 23 Table of Contents Abstract............................................................................................................................................ 0 List of Figures .................................................................................................................................. 1 List of Tables ................................................................................................................................... 1 Table of Contents ............................................................................................................................ 2 Table of Contents ............................................................................................................................ 2 Problem Statement.......................................................................................................................... 1 Purpose ........................................................................................................................................... 1 Background...................................................................................................................................... 1 Metal Matrix Composites............................................................................................................. 1 Types of Metal Matrix Composites.............................................................................................. 2 Fiber Reinforced MMCs .......................................................................................................... 2 Particulate Reinforced MMCs ................................................................................................. 3 Tensile Strength and Young’s Modulus ...................................................................................... 5 Particle Distribution ..................................................................................................................... 9 Broader Impacts ............................................................................................................................ 10 Procedure ...................................................................................................................................... 10 Testing Overview....................................................................................................................... 10 First Sample Set – Gravity Cast Samples................................................................................. 11 Sample Preparation .............................................................................................................. 11 Second Sample Set – Gravity Cast Tensile Samples............................................................... 12 Sample Dimensions .............................................................................................................. 12 Tensile Testing...................................................................................................................... 13 Analysis................................................................................................................................