Improving the Fracture Toughness of Friction Stir Welding Tools
Abstract
The proposed research will advance the current state of the art of friction stir welding (FSW) tool materials. The key aspects of the study will be: 1) material selection; 2) fabrication; 3) mechanical evaluation of test coupons of fibrous monolithic (FM) materials; 4) fabricate and evaluate FM friction stir welding tools. The project will utilize thermodynamic modeling to evaluate material compatibility and the co-extrusion technique to fabricate FM test articles and FSW tools. This research has the potential to improve the efficiency of current FSW tool technology and open the door to new materials previously unweldable by state-of-the-art FSW techniques.The goal of the proposed project is to improve the fracture toughness and wear behavior of friction stir welding (FSW) to"ols over those which are currently available. Hardness, toughness, and wear resistance are of paramount importance to producing a s""uccessful FSW tool. Compared to pure metals and alloys, ceramic materials exhibit higher hardness, up to ~45 GPa1 for cubic boron n"itride (cBN) and on the order of 100 GPa2 for diamond. This high hardness lends itself to high erosive and abrasive wear resistance". However, the toughness of ceramic materials is generally low, on the order of ~3 MPa~m~. The result of this toughness is that co""mpared to metals and alloys, ceramics show little damage tolerance and tend to fail catastrophically once cracks or other damage are"" initiated. As the envelope of materials being friction stir welded has expanded to include high strength steels, titanium, and oth""er exotic alloys the high temperature capabilities of FSW tools has become more important.Here again, ceramics and ceramic composite"s generally maintain their properties to higher temperatures than metals and alloys. Unfortunately their lack of toughness and damage tolerance lead to the potential benefits of ceramic tooling going largely unrealized. Engineered architectures such as fibrous" monoliths (FMs) possess a unique combination of properties well suited to applications such as FSW tooling where the hardness, wear"" resistance, and high temperature capability of the ceramics are needed but higher damage tolerance is required. FMs are a category" of materials with an engineered architecture at the macroscale (10~s to 100~s of microns) wherein the composite is composed of hard", strong, wear resistant cells surrounded by a weaker cell boundary phase. The weaker cell boundary phase deflects and arrests crac""ks, not allowing them to pass easily from one cell to the next. This arrangement allows the overall composite to exhibit the benefi"cial properties of the cell material while at the same time increasing its damage tolerance. Abstract: The goal of the proposed project is to improve the fracture toughness and wear behavior of friction stir welding (FSW) tools over those which are currently" available. Hardness, toughness, and wear resistance are of paramount importance to producing a successful FSW tool. Compared to pur""e metals and alloys, ceramic materials exhibit higher hardness, up to ~45 GPafor cubic boron nitride (cBN) and on the order of 100"" GPa for diamond. This high hardness lends itself to high erosive and abrasive wear resistance. However, the toughness of ceramic ma""terials is generally low, on the order of ~3 MPa~m~. The result of this toughness is thatcompared to metals and alloys, ceramics sh"ow little damage tolerance and tend to fail catastrophically once cracks or other damage are initiated. As the envelope of materials" being friction stir welded has expanded to include high strength steels, titanium, and other exotic alloys the high temperature cap""abilities of FSW tools has become more important. Here again, ceramicsand ceramic composites generally maintain their properties to" higher temperatures than metalsand alloys. Unfortunately their lack of toughness and damage tolerance lead to the potential benefi"ts of ceramic toolin
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 05, 2017
- Source ID
- N000141712572
Entities
People
- Jeremy Watts
Organizations
- Office of Naval Research
- United States Navy
- University of Missouri System