Advanced Manufacturing Technologies for Boron-rich Materials for Extreme Environments

A overview of this R&D program, including more recent developments, was presented at the EUROMAT2005 Conference in Prague, Czech Republic, in September 2005 and can be downloaded from the Web site of ExtreMat, the European partnership on materials for extreme environments. The link to the presentation is:

 2005 OVERVIEW
 

Technology for Near Net-Shape Casting of Boron-rich, Advanced Ceramic Components

HY-Tech Research Corporation is collaborating with national laboratories and universities to develop pressureless casting of greenware and microwave-based sintering for boron-rich ceramics. This technology is expected to lead to cost-effective manufacturing of engineered ceramics for use in extreme environments, including aerospace applications.

A recent summary of this work with emphasis on aerospace applications can be found at

 NASA MIRROR TECH DAYS 2005 PRESENTATION

The ceramic processing R&D program (together with the partnerships and collaborations that are making it possible) is an outgrowth of the boron-based coatings development programs described below:

Technology for Boron-based Advanced Ceramic Coatings

HY-Tech Research Corporation has demonstrated a  method for reliable cathodic arc (alias vacuum arc) deposition of boron carbide (B₄C) coatings from a pure, solid, comsummable B₄C cathode (feedstock). This patented method, allows the application of vacuum arc technology, known for its robustness, commercial scalability and high-deposition rates to B₄C an important ceramic coating, known for its chemical inertness, low weight, high-temperature, high hardeness and good thermal and electrical conductivities. The method can be extended to other similar ceramic coatings, such as titanium diboride, also an important hard-coating.

With support from the Department of Energy (DOE) through the Small-Business Technology Transfer Research (STTR) Program, HY-Tech has demonstrated deposition of amorphous boron carbide (a-B₄C) from a solid B₄C cathode. Innovative cathode preparation and handling has allowed for operation without damage to this otherwise brittle material. Some key aspects of this work can be found in

 FUSION TECHNOLOGY, VOL. 39, MAR. 2001, pp. 910-915.(a journal of the Americal Nuclear Society; a reprint can be downloaded here; it is about 1.2MB) 

and

JOURNAL OF MATERIALS SCIENCE, VOL. 38 (2003) pp. 3117-3120

 The partner institution in the original  STTR project was the Plasma Application Group of the Lawrence Berkeley National Laboratory (LBNL), a research group known for seminal work in the field of cathodic arc plasma discharges and deposition.  All the film characterization during the DOE project was done by this group.

 The obtained B₄C coatings are in a dense, amorphous form, such as desired for numerous hard-coating and tribological (low-friction) applications. On metal substrates, judicious control of the electric bias has led to hardness values approaching those of bulk, crystalline B₄C, but with a low modulus (==> a high impact resistance).  Used either on alone or as part of multi-layer (or nanostructured) coatings, this material can extend the life of tools and components and is compatible with high temperature applications (up to 2300°C).

Commercially, such dense, amorphous B₄C coatings are obtained only through standard Physical Vapor Deposition technologies, such as magnetron sputtering. The vacuum arc offers the possibility of much higher deposition rates. HY-Tech Research is interested in industrial partnerships to further develop the new technology into a commercial product.

Technology for  Amorphous Boron Coating Deposition

 HY-Tech Research Corporation has developed a cathodic arc-based technology ( HYBron™) for the deposition of super-hard, high impact resistance amorphous boron coatings. As an outgrowth of the DOE B₄C program and additional support from the National Science Foundation (NSF) through its Small-Business Innovative Research (SBIR) Program, HY-Tech has demonstrated operation of a cathodic arc (in vacuum mode) with a super-pure, sintered boron cathode. Innovative, patented cathode preparation and handling has allowed for operation of the arc discharge with this non-metal (in fact, a semiconductor at room temperature) cathode material.

Boron (B) holds great promise for advanced materials applications. It is the hardest elemental material other than diamond. It also has the prospect of being self-lubricious, because the surface oxide can react with atmospheric moisture to form boric acid, a solid lubricant, which works somewhat in the same way as graphite. Boron is also one of the lightest materials and is resistant to corrosion by acids. Its wear-hardening and its refractory properties make it ideal for high temperature applications, such as advanced automotive engines.

 HY_Tech's boron coatings fall in the category of the boron sub-oxides,  a class of materials having a stoichiometry B_xO, x>>1 (typically x=11 or 22). In the NSF SBIR project, HY-Tech collaborated with researchers at the Oak Ridge National Laboratory (ORNL), the first laboratory to successfully synthesize these advanced materials in the form of coatings. HY-Tech's cathodic arc technology brings a more commercially scalable technology into the synthesis of these super-hard materials.

In the past, ORNL's Surface Modification and Characterization Laboratory performed most of the surface analysis for HY-Tech, using their world-class ion beam facility.  Currently most of this facility has been moved and reassembled at the Center for Irradiation of Materials (CIM) at the Alabama A&M Research Institute (AAMURI). Research is presently continuing in collaboration with AAMURI/CIM's team, as well as with researchers retired from the original ORNL facility.

The coatings have all been produced at HY-Tech's R&D facilities. Adherent coatings have been produced this far on 52100 steel, CP-Ti, Ti-6-4, Cr-plated steel, and even Al alloys (except in salt corrosion environments, for the case of Al alloys). Rutherford Backscattering (RBS) of the deposited films show mostly pure boron, except for ~6 at.% oxygen (which gives the sub-oxide composition and a much higher impact resistance that pure amorpous boron). RBS found no significant traces of C or metal impurities. Low-C is important because it can adversely affect the hardness.

 More details on the properties and a discussion on the originally envisioned, commercial applications for this coating can be found in

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, Volume 20, Issue 3 (May 2002) pp. 725-732

The results of a test study on a specific commercial application (life-extension of steel dies used in aluminum die-casting) can be found in this downloadable document:

"Copyright © 2004 Society of Vacuum Coaters, Inc.  All rights reserved.  No part of these materials may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system without permission in writing from the Society of Vacuum Coaters, Inc.   
 

Die Casting Study**

**This work is reproduced here with permission from the Society of Vacuum Coaters.  This work was presented at the 47th Annual Technical Conference, Society of Vacuum Coaters, April 24-29, Dallas, TX.  The Proceedings of this conference will be published fall 2004 and can be ordered from the SVC by sending an E-mail to svcinfo@svc.org or by completion of the SVC publications order form on the SVC Web Site at http://www.svc.org."
 

 The paper describes testing  performed by use of the "Soldering and Thermal Fatigue Test Unit" of the Melting and Casting Laboratory in Metals and Ceramics Division at Oak Ridge National Laboratory.  One of figures shows a totally solder-free region of a HYBron™-coated H-13 steel sample after 50 cycles of testing in the aluminum alloy casting environment. HY-Tech Research is interested in industrial partnerships to further develop the new technology into a commercial product for applications including, but not limited to aluminum alloy die-casting..