{"id":28290,"date":"2016-03-29T13:58:19","date_gmt":"2016-03-29T13:58:19","guid":{"rendered":"https:\/\/www.padtinc.com\/2016\/03\/29\/reactivity-of-metal-alloys-in-metal-3d-printing\/"},"modified":"2022-03-31T16:51:47","modified_gmt":"2022-03-31T23:51:47","slug":"reactivity-of-metal-alloys-in-metal-3d-printing","status":"publish","type":"post","link":"https:\/\/www.padtinc.com\/2016\/03\/29\/reactivity-of-metal-alloys-in-metal-3d-printing\/","title":{"rendered":"Reactive and Non-Reactive Metal Alloys in Laser-based Powder Bed Fusion"},"content":{"rendered":"

One of the first concepts\u00a0you come across in metal 3D printing is the notion of reactivity of the powder metal alloys – in this post, I investigate\u00a0why some of these powder alloys are classified as reactive and others as non-reactive<\/strong>, and briefly touch upon the implications of this to the user of metal 3D printing tools, scoping the discussion to laser-based powder bed fusion. Ultimately, this boils down to a safety issue and I believe it is important that we, the users of these technologies, truly understand the fundamentals behind the measures we are trained to follow.<\/p>\n

Figure 1 below is indicative of the range of materials available currently for the laser-based powder bed fusion process (this selection is from Concept Laser). I have separated these into non-reactive and reactive metal alloys. The former includes steels, Inconels, bronze and CoCrW alloys. The reactive metal alloys on the other hand are Aluminum or Titanium based. The question is: what classifies them as such in the context of this process?<\/p>\n

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Figure 1.<\/strong>\u00a0Typical metal alloys available for the laser-based powder bed fusion process (from Concept Laser), classified as Non-Reactive and Reactive<\/figcaption><\/figure>\n

Reactivity in this process really pertains to the likelihood of the alloy in question serving as a fuel for\u00a0a fire and\/or an explosion, which are two related but distinct phenomena. To\u00a0truly understand the risk associated with powder metals, we must first understand a few basic concepts.<\/p>\n

1. Fire and Explosion Criteria<\/h2>\n

Figure 2 is a commonly used representation of the criteria that need to be met to initiate a fire (fuel, oxygen and an ignition source) and an explosion (the same three criteria for a fire, plus a dust cloud and confined space). When handling reactive metal alloy powders, it is important to remember that two of the three requirements for a fire are almost always met and the key lies in avoiding the other criterion<\/em>. When not processing the powder in the machine, it is often subject to ambient oxygen content and thus all precautions are taken to prevent an ignition source (an ESD spark, for example). When the metal is being processed with a high power laser, it is done in an inert atmosphere at very low Oxygen levels. This thought process of appreciating you are one criterion away from a fire is useful, if sobering, to bear in mind when working with these powders. Well in case of fire explosion which can harm that should be resist or plan to resist.<\/p>\n

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Figure 2.<\/strong> The fire triangle and explosion pentagon<\/figcaption><\/figure>\n

2. Terms Used to Describe Fire and Explosion Risk<\/h2>\n

There are several terms used to describe fire and explosion risk. I have picked 5 here that tie into the overall “index” I will discuss in the following section.\u00a0All these parameters are in turn functions of the material in question, both with regard to its composition and its size distribution and are co-dependent. These definitions are adapted\u00a0from Benson (2012)<\/a>\u00a0and Prodan et al. (2012)<\/a>.<\/p>\n