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Novel Ceramic/Metallic Materials May 2017 Viewpoints

Technology Analyst: Cassandra Harris

3D Printing Metallic Glass

Why is this topic significant?

The fabrication of metallic glasses is a barrier to their use in a variety of applications. Exmet is developing 3D-printing technology that could accelerate the commercialization of metallic glasses.

Description

In March 2017, Exmet (Stockholm, Sweden) announced an investment agreement with AM Ventures (Gräfelfing, Germany) to accelerate the development of Exmet's 3D-printing technology for the fabrication of metallic glasses—metals and alloys with a disordered glass-like crystal structure. Exmet's 3D-printing technology uses electron-beam melting (EBM)—a process that selectively melts metal powder layer by layer using an electron beam. It also incorporates a cooling system to cool the material rapidly after it has melted so that it solidifies with a disordered crystal structure. Exmet claims that its technology can also fabricate metallic-glass composites (see the May 2016 Viewpoints), compositionally graded metallic glasses, and structurally graded metallic materials that incorporate metallic glass and crystalline metallic phases. Exmet first demonstrated its technology in 2016.

Implications

Researchers prepare metallic glasses by rapidly cooling a liquid metal or alloy using near-net-shape forming techniques such as casting, melt spinning, or thermoplastic forming. The fabrication of metallic glasses with dimensions greater than about 1 millimeter—so-called bulk metallic glasses (BMGs)—by means of conventional techniques is challenging because the cooling rate of the liquid metal necessary for it to form a disordered crystal structure increases as the dimensions of the material increase.

3D printing is a bottom-up approach to fabricating BMGs; because researchers fabricate the BMG sequentially in millimeter-scale sections, the cooling rate necessary for it to form a disordered crystal structure is low and simple to produce. Similar bottom-up approaches to BMG fabrication exist—such as various welding and joining techniques—although these techniques have mostly had demonstration at an academic level. A potential limitation of using EBM to fabricate BMGs is the formation of cracks at the interfaces of the individual 3D-printed sections, which occurs in BMGs prepared by means of welding and joining techniques. Further research is most likely necessary to characterize the properties of BMGs fabricated by means of EBM.

Impacts/Disruptions

Metallic glasses display high strength, high hardness, and high resistance to wear and corrosion. They find use in medical devices, electronic devices, and sports equipment. Metallic glasses are also attractive candidate materials for use in the engineering, construction, defense, and aerospace industries. However, the fabrication of metallic glasses remains a barrier to their widespread commercialization.

3D printing may prove an effective method of fabricating metallic glasses more rapidly than conventional fabrication processes and at lower cost. It could also potentially accelerate research and development of metallic glasses and open new applications of metallic glasses.

Scale of Impact

  • Low
  • Medium
  • High
The scale of impact for this topic is: Medium

Time of Impact

  • Now
  • 5 Years
  • 10 Years
  • 15 Years
The time of impact for this topic is: 5 Years

Opportunities in the following industry areas:

3D printing, automotive, aerospace, construction, defense, electronics, energy, medical, sports equipment

Relevant to the following Explorer Technology Areas:

Flexible Silicon Electronics

Why is this topic significant?

Researchers have developed a flexible silicon substrate using a novel design approach. Flexible silicon could pave the way for advances in flexible electronic devices.

Description

In March 2017, researchers at the King Abdullah University of Science and Technology (KAUST; Thuwal, Saudi Arabia) published research describing the development of a flexible silicon substrate that can bend and stretch to more than five times its normal area. The substrate comprises monocrystalline-silicon "islands" with a thickness of 500 micrometers (µm), interconnected with flexible monocrystalline-silicon "springs" with a thickness of 30 µm. The researchers claim that the silicon islands provide the substrate with mechanical stability, and the springs give it flexibility. The researchers fabricated the substrate by first patterning a silicon dioxide wafer using photolithography and reactive ion etching and then exposing the wafer to a reducing agent in order to remove oxygen and convert its composition to elemental silicon. Their research appeared in the scientific journal Applied Physics Letters.

Implications

Researchers have developed flexible silicon and other flexible materials such as ceramics and glasses (see the March 2016 Viewpoints and the November 2015 Viewpoints) that are ordinarily rigid and brittle by reducing the thickness of these materials to several micrometers. However, ultrathin materials have low mechanical strength and are extremely fragile, and therefore the number of practical applications of ultrathin materials is limited. The researchers at KAUST have developed an entirely different approach to flexible silicon. As a result, the researchers have developed a flexible silicon substrate that is much thicker than conventional flexible silicon substrates. Because the researchers used complementary-metal-oxide-semiconductor (CMOS) processing technology to fabricate the substrate, opportunities could exist to use CMOS processing for the fabrication of other flexible inorganic substrates that comprise metal oxides or other elemental semiconductors with various thicknesses.

Impacts/Disruptions

Flexible silicon is in its infancy, and much research and development is necessary before flexible silicon makes a significant commercial impact. Nevertheless, the KAUST researchers' findings are significant, because they could pave the way for flexible silicon electronics or solar cells that find use in a multitude of applications. Flexible electronics are attracting considerable research interest, but researchers are focusing their efforts on the development of printed electronics that incorporate plastic substrates. Although plastic substrates are low in cost and have inherent flexibility, the thermal stability and electrical properties of plastic substrates do not rival those of silicon, and the fabrication of printed electronics is incompatible with the CMOS technologies of today's semiconductor industry.

Scale of Impact

  • Low
  • Medium
  • High
The scale of impact for this topic is: Medium to High

Time of Impact

  • Now
  • 5 Years
  • 10 Years
  • 15 Years
The time of impact for this topic is: 5 Years to 10 Years

Opportunities in the following industry areas:

Consumer electronics, micromachining, photovoltaics, semiconductor

Relevant to the following Explorer Technology Areas: