difference between 伤痕， 伤疤 and 疤痕？
Often "疤痕" is reserved for "physical scar", while "傷疤" and "傷痕" can mean more; they can even mean a mental scar.

Therefore, being a 疤痕 implies being a 傷疤 (resp. 傷痕); being a 傷疤 (resp. 傷痕) not necessarily implies being a 疤痕.

Nevertheless, please bear in mind that these distinctions are subtle and not dogmatic. :)