Hi
I am afraid that you are not able to use DAX to transfer binary data to another format string.
Based on my test, when I import SQL Server table which contains binary data to Power BI Desktop, even if I can see the binary data column in Query Editor of Power BI Desktop, the column is removed from the resulting table in Data view and Report view, as shown in the following screenshot. 
As stated in this article, this binary data type column is currently not supported in Power BI Desktop, and an idea about this issue has been submitted in this link, please vote it. In your scenario, you would need to change the data type of primary keys columns in the original data source.
Thanks,
Lydia Zhang