Gas, Gas Turbines, O&M, Renewables

The Additive Age

Issue 7 and Volume 121.

BY PAUL BROWNING, CEO AND PRESIDENT OF MITSUBISHI HITACHI POWER SYSTEMS – AMERICAS (A part of MITSUBISHI HEAVY INDUSTRIES Group)

Materials Science and Engineering has provided the chapter titles in the book of human history: The Stone Age, the Bronze Age, and the Iron Age. Although all fields of science and engineering are important, it is the advancements in materials science that have marked critical eras of human advancement. When I was studying Materials Science and Engineering as an undergraduate at Carnegie Mellon University, I wondered whether, hundreds or thousands of years from now, historians would say we are currently in the Silicon Age due to the transformational emergence of the silicon transistor chip. But in recent years, I’ve concluded the history books will label this the “Additive Age”.

I say this because it’s actually a form of additive materials technology that enabled the modern silicon transistor chip. These chips are printed on large single crystal disks of silicon. When most materials turn from liquid to solid, the atoms arrange themselves into small “crystals” that all have the same geometric orientation relative to one another. Many of these small crystals grow together to form a solid material composing many small crystals of varying orientations. The boundaries between these crystals can cause microscopic variations in important material properties, such as electrical conductivity.

The latest Thermal Barrier Coatings are applied layer by layer with a high velocity high temperature Plasma Spray process on the component surface.
The latest Thermal Barrier Coatings are applied layer by layer with a high velocity high temperature Plasma Spray process on the component surface.

About six decades ago, Materials Scientists discovered, under very controlled conditions, they could create a “single crystal” by starting with a seed crystal of the desired orientation and then controlling solidification so that a larger crystal was formed by solidifying one layer of atoms at a time and “growing” the desired object. This allowed scientists and engineers to make single crystal wafers with atomically uniform electrical properties that were ideal substrates for very small transistors – thus the silicon chip was born. This depositing of one layer of atoms at a time was one of the earliest forms of additive manufacturing.

And as additive manufacturing enabled the computer chip, the computer chip enabled greater computational power, which allowed Materials Engineers to extend additive manufacturing not only to lithographic printing of ever smaller p-n junctions on single crystal silicon, but also to many other applications.

It’s been almost 30 years since I graduated from CMU, and I’m now president & CEO of a company that manufactures some of the largest, most fuel efficient gas turbines in the world. We make extensive use of additive manufacturing in the development of turbines. For example, we use the same single crystal technology that was developed for silicon chips to manufacture large turbine blades that are directionally solidified. This means we start with several seed crystals and grow them all in one direction so that the boundaries between them are all oriented along the major stress axis of the blade. In our case, we’re worried about the strength of those boundaries at a high temperature. By orienting the grain boundaries in this way, the life of our turbine blades at higher temperatures can be maximized. In addition, we use additive manufacturing to deposit ceramic coatings on many of the cooled components in our turbine. Through a process called plasma spraying, these coatings are deposited one layer at a time. They then act as insulating “thermal barriers” between the very hot gasses that flow through the turbine and the alloys the components are made from. These additive technologies are critical to improving fuel efficiency, which has enabled a dramatic reduction in carbon dioxide emissions in the latest generation of power plants versus the older coal-fired power plants they often replace.

More recently, we have begun to use additive technology to “print” components for gas turbines. Today, we’re able to print these same components in three dimensions, by using lasers to solidify powders, one layer at a time, in a complex three dimensional pattern. Using 3D printing, we can rapidly prototype new designs we want to test, and we can even print production-ready parts.

We now see additive technology expanding into many industries, and being used for a wide range of plastic, metallic and ceramic materials. And it’s all made possible by the original additive technology, which enabled the modern computer chip.

So welcome to the Additive Age of human history. In the coming years, we’ll see many new uses of additive technology.