Baotou Xidi Pilots New Method for Producing High-Coercivity NdFeB Magnets
New method combines physical vapor deposition and grain boundary diffusion
In late-2018, Baotou Xidi Rui Technology (“Baotou Xidi”) piloted production of NdFeB permanent magnet alloy using a new technique that increases magnet coercivity (resistance to demagnetization) versus conventional manufacturing methods.
The new technique employed by Baotou Xidi combines two well-known methods for boosting coercivity – physical vapor deposition (“PVD”) and grain boundary diffusion (“GBD”) – methods that have been individually employed by Japanese magnet manufacturers for years, but, to our knowledge, never together.
High coercivity is important for high-performance applications such as EV traction motors
Simply put, coercivity is the measure of a magnet’s resistance to demagnetization when exposed to elevated temperatures and/or strong demagnetization fields.
Traditional methods for increasing coercivity of NdFeB magnets involve the partial substitution of neodymium with dysprosium and/or terbium in the magnetic alloy. This practice can more-than-double the maximum operating temperature of NdFeB, from 80C to upwards of 200C, but is not without its drawbacks.
A downside of partially substituting neodymium for dysprosium and/or terbium is that the latter two metals dilute the strength of the magnet into which they are added, meaning an end-user needs to use a larger and heavier magnet for a given application than they would if temperature and/or demagnetization were of no concern.
Enter PVD and GBD – techniques to that increase coercivity while minimizing dilution
To minimize the dilution associated with producing high coercivity NdFeB magnets, manufacturers in Japan (such as Hitachi, TDK and Shin-Etsu) have developed and employed an array of PVD and GBD methods for manufacturing high coercivity magnets with 20% to 60% lower concentrations of dysprosium and/or terbium.
The new method piloted by Baotou Xidi involves vapor deposition of dysprosium and/or terbium onto the surface of the magnet substrate by sputtering, followed by high-temperature vacuum diffusion of the dysprosium and/or terbium into the grain boundaries of the magnet substrate.
According to Dr. Song Zhenlun, a researcher at the Ningbo Institute of Materials Science, and the inventor of the aforementioned process, the technique can increase the coercivity of NdFeB products by two to three grades, while reducing the amount of dysprosium and/or terbium required by 60% to 70%.
Given the pronounced decline in global dysprosium (and terbium) production since 2013, coupled with explosive demand growth for electric vehicle traction motors, windpower generators, industrial robots, and other end-uses of high-coercivity NdFeB, Adamas Intelligence believes that if not for the above-described techniques, the global market would currently be facing substantial dysprosium (and possibly terbium) shortages.
Looking ahead, we believe PVD, GBD and other manufacturing techniques, such as grain size refinement (“GSR”), will be key to balancing global supply and demand of dysprosium and terbium as electric vehicle production continues to skyrocket.
Market outlook to 2030
For a detailed breakdown of global rare earth production, consumption and trade – and forecasts to 2030 – keep an eye out for Adamas Intelligence’s upcoming ‘Rare Earth Market Outlook to 2030’.
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